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Community and Q&A

Mystery Noise Coming from Interior Wall

tdjanke | Posted in General Questions on

About 2 months ago we started to hear a strange knocking coming from an internal wall in our house. The knock usually occurs in the middle of the night but sometimes it happens in the evening and sometimes in the morning.

There were here a few theories we had…

1. HVAC expanding/contracting – our neighbors have the same model and have opened this wall up before in their house, no vents

2. Water pipes- again, neighbors report no pipes

3. Expansion / contraction – this is our last idea left but have no way to verify nor anything to fix.

We are able to catch the sound on our cameras so I posted one to this thread. Usually it’s a double knock but sometimes it’s a single one. And ideas on on how more precisely troubleshoot this to work toward a fix would be appreciated!

reference: location is Orange County CA so daytime is usually low 70’s and night is mid to upper 50’s. Basically some of the least extreme temp swings one could

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  1. GBA Editor
    Martin Holladay | | #1

    Ghost? I really have no idea.

  2. Expert Member
    Zephyr7 | | #2

    The first thing for you to do is to try to see if the sounds align in time with anything outside. Does the sound occur when the outdoor temperature changes some amount (or more? Does the sound occur when the sun starts to hit the wall? When the sun stops hitting the wall? When you run the hot water? When the heat or air conditioning starts, or stops?

    If you have sounds from water pipes, the sound should align with running probably hot, or maybe cold water. The sound may lag when you actually run the water by a few minutes since the pipes need to either get hot or get cold before they will expand or contract enough to make a sound.

    In my expierience, pipes tend to make a “bang twang” kind of sound. Ductwork makes a hollow sound like tapping a piece of sheet metal. Wood and other similar materials makes more of snapping sound. Experience helps a lot to get an idea what make actually be making any other sound.

    I’d also check to see if there is anything loose that may be blowing around in the wind and hitting the wall at times. The other possibility is an animal, like a mouse, getting into a wall or crawl space. Mice tend to jump, and when they land on something (like a duct) after jumping you might here a sound.

    It’ll take some investigation to localize the source of the sound. The key is to be methodical, and be observant to try to match up events you see or hear with the sound happening. That will help lead you to the cause.


    1. tdjanke | | #3

      Hi Bill,

      There is no correlation with anything. We’ve seen it happen in the early evening but often happens between 10pm and 5am. The first night this happened it was very windy (Santa Ana winds were coming through the area) but that only lasts 1 week but the sounds continue. Last night it happened at 11:30pm and again at 4:30am this morning. This doesn’t sound hollow or like a twang but like something banging into wood.

      In Cali we have fire sprinklers in the ceiling so that became my latest suspect. To test I moved my cameras into the dining room where the sound comes from with 1 by the wall where we think it is and the other on the ceiling near the sprinkler head. The sound is not coming from the ceiling we found out. Next step is the put the cameras near different locations on the wall to narrow in on the exact spot.

      We’re getting closer to the location but the sound doesn’t sound like pipes, vents or rodents but I hope I’m wrong because I’m running out of causes. If anything else comes to mind, I’m all ears.

      1. Expert Member
        Zephyr7 | | #4

        I’d say it might be woodpeckers, but they’re not usually active at night.

        If it’s random, and at night, I’d suspect vermin of some sort. Some kind of nocturnal critter. Look for signs of chewing and other damage on the exterior, especially any concealed or sheltered areas (under eaves, behind bushes, etc). Check all your roof vents. Check in the attic too (but be careful, you don’t know what you might find hiding in there).


  3. Roger Berry | | #5

    Not sure how there might be a sufficiently large hole in the wall's top plate, but maybe the rodent idea has some merit. They cache seeds and nuts, sometimes in large quantities. Perhaps the randomness of the thumps is related to activity in the pile. If it is resting near a hole for wire, sprinkler pipe or just a misplaced hole, random seeds or nuts might be dropping into the wall and hitting the base plate and perhaps a piece of blocking on the way down. That might account for the one or two knocks. Do you have seed or nut bearing bushes or trees?

    If it is a critter, I recommend Reese's Pieces as bait for live trapping. Raccoons like them very much, so I guess chipmunks and squirrels will too.

    1. kjmass1 | | #6

      I like this theory. At first watch it startled me with it being so loud- I was expecting much less.

      Hearing it a second time, it does sound like an acorn falling from 10’, although the second knock seems too quick on the rebound.

      I had a woodpecker on the metal cap of my chimney- the whole house echo’d like nothing I’d ever heard before.

      1. Expert Member
        Zephyr7 | | #7

        An acorn would probably fit through an empty hole made to run wire. Those holes are usually 5/8” or 3/4”.

        If the acorn fell and hit an electrical box or som blocking, it might make multiple quick knocks.

        I know from experience in my own house that if critters are borrowing in your insulation, you’ll probably need to replace it. I’m picking up some mineral wool batts tomorrow to replace mouse damaged fiberglass.


  4. Walter Ahlgrim | | #8

    Food for thought Truss uplift

    No very likely given how little difference you have from high to low temp.


  5. tdjanke | | #9

    Usually it’s a double knock but not always the same delay between knocks. And then sometimes it’s a single knock.

    I have no trees above my house to drop acorns in either.

  6. Jsrtmc | | #10

    Tdjanke, I realize this is an old forum, but did you ever resolve where this sound was coming from? We are hearing same sound on our Wyze cameras?

  7. Roger Berry | | #11


    Back again with a possible alternative to rampant rodents. I have heard trusses pop now that I have them. A combination of moisture and heat differences will make them move just enough on the top sills to make their complaints heard. At least, I hope the join plates are the source.

    I should have thought to pose the idea of truss movement before, as I have had to re-screw drywall ceilings that had many of the screws pulled through the drywall by truss members lifting aggressively. I suggest looking for little splits in the corners of wall to ceiling near where you hear the banging if you also have trusses. They can move when the sun goes across a roof and the shadow side cools faster. Metal roofs are also quite "poppy".

  8. Deleted | | #12


  9. gotsameknocking | | #13

    Hello I hope someone can answer your question regarding the knocking because - we live in the Midwest and have the same problem in fact we have called the police they only listened to it with no response as to what it was, we called the fire department - (the fire department thought it was water hammer) they went through every part of my all electric condo - we called 2 different plumbing companies both plumbers said it was not water hammer so that was a 400.00 bill then we called HVAC service man (another 90.00) he turned off the air flow to the house and said it’s not my ducts. My neighbor thinks it’s my kids but usually each time the sound is heard we are all together. We are running out of money and ideas so maybe there is a logical explanation- I have attached a video for the audio any Logical ideas on where to go next will be appreciated - Thank you

    1. Expert Member
      Akos | | #14

      That sounds like pipe expansion noise. Water and drain lines expand when they heat up, sometime if not well supported or tight through a stud it makes that sound as it heats up or cools down. Very hard to find and fix as it carries through the structure.

  10. Expert Member
    Zephyr7 | | #15

    Might be pipe expansion noise. It’s really hard to tell. Pipes generally make noise when they change temperature quickly, usually when you start running the hot water. If the sound seems to be loudest near an exterior wall, I’d suspect the gutters might be the source of the noise.

    What you need to do is try to find it where the sound is strongest, then think about what materials in that particular area might be expanding/contracting to cause the sound. Think about pipes, gutters, siding, etc. It’s very unlikely this noise is coming from wiring. Critter noise tends to be more random, so my guess would be thermal expansion (from something warming up) or contraction (from something cooling off). If the sound happens in the morning or evening, it’s probably something on the exterior of your home. If the sound happens when someone uses a sink or shower, that’s probably water pipes. Find the area of the sound first, then take note of what time it happens most frequently, then think about what in that area is going on at that time and you can start to get closer to finding the cause.


  11. gotsameknocking | | #16

    Thanks for the insight we have another appointment for another plumber to come out Monday to test the pressure by turning off the water from the street. But now maybe we will Cancel the plumber appointment and look for a good maintenance man - our HOA should help with this thanks again

    1. Expert Member
      Zephyr7 | | #18

      Pressure causes water hammer. Water hammer happens when you open or close (usually close) valves like faucets. Water hammer is usually one big BANG or BOOM, not a “tick, tick, tick” sound. The cyclic ticking is usually thermal cycling.

      I have sometimes used a one or two sizes too big pipe clamp with a wrap of rubber sheet around the pipe with the clamp over that. This can help damp vibrations. Thin sheets of rigid polyethylene can help on horizontal runs since it acts like a linear bearing.

      Another thing that can help quiet down pipes is to rigidly clamp the pipe periodically with the clamp-over-rubber arrangement I described earlier. When doing this, you’ll get the best results if you’re clamps aren’t perfectly evenly spaced. Even spacing can allow resonances. Resonances will be damped if the clamps are all spaced at slightly different intervals. Don’t clamp at halves, either, use odd multiples like 1/3, 3/5, etc. The goal is to maximize the vibration damping.


  12. Roger Berry | | #17


    Well, back to add a guess. Your sound has a soft start then three major peaks. The lifting truss noise I have heard is more often than not a single bang. Fairly sharp definition, no repeats. The CPVC piping I had in an early home would make a fairly long series of "tik tik tik tik" when drawing hot water. I greased the plastic clips that held the pipe and all went quiet. The big PVC drain that passed through a joist and dragged a bit sounded much the same, only lower pitch. Teflon tape slipped under the contact point fixed that.

    The sound you have recorded and presented leads me to guess a partial plugged vent or trap that is being emptied in a cyclic manner, perhaps through suction effect. Are you new to the home or later owner? Any memories of toys or clothing that got sent down the plumbing by accident?

    I am basing this guess on two incidents I had with bad plumbing in an old house. The first was an ice cap on my vent stack one winter long ago when the temperatures fell far below zero. The toilets started flushing most oddly with burbles and gulps that confused me. It seemed like a pressure balance issue, so I checked the vent stack and sure enough it was almost totally closed by ice that had formed by freezing the moist vent air from baths and showers meeting sub zero air in a iron pipe. Clearing the pipe cleared the problem. The second was a bathtub with a long horizontal drain with nearly zero pitch ending in a drum trap. Years of hair and goo had reduced the cross section so severely that draining the tub took ages and it would often go "bloop, bloop, bloop" as it drained.

    The tests I would suggest, if a one story house, is run sink, toilet, tub in separate cycles to see which one sets off the thumps. It may be several minutes between running water and the sound appearing. If more than one bathroom, start with the one furthest from the vent stack if you can determine where that is. For a two story, check the upstairs sink, then tub, then toilet, waiting several minutes between each fixture.

    It is barely possible that a bird or squirrel fell down the vent, but they usually rot fast enough to not make the problem last that long. My guess is you will find a toy or fabric wad stuck in a vertical pipe that holds water back long enough to make the air bubble burst up through the water column and go "bloop, bloop, bloop" like the taped noise. If you have a basement where the long horizontal runs can be felt with your hands, then maybe the long pipes are where the water is stacking up and the vertical vent is just carrying the bloop noise upward. Hope you don't have a slab house.

    You didn't say what your weather is, but no place in the US has sub-zero temps at the moment so I'm guessing toys, socks or hair globs. If you have a two story house, the vertical vent line can also be a drain line. I think it is called a wet vent. Others better at plumbing might want to weigh in on how the lines might be installed incorrectly or where to best look for a partial plug.

    If you have any sense of the plumbing runs and connection points, try focusing your attention on those areas. If you are really into detective work, a cheap stethoscope might be money well spent.

  13. Wooba Goobaa | | #19

    Maybe try an IR camera or endoscope to determine what is in the walls?

  14. MrFussy | | #20

    I just discovered this thread, and thought for a moment I had posed the original question. I'm not sure if OP solved the issue. I have the metallic, echo-ey knocking behind the plaster and drywall of my bedroom - far from any pipes or heating. So that would seem to rule out the water hammer, though I'm happy to try. I can hear it inside, but if I stand by the exterior wall on the patio, I can't hear it unless I put a glass to the stucco. It seems to be wind-sensitive for some reason, but not consistently. Today it's breezy, and the noise seems louder than last night when it was much windier. My house is cantilevered from the hillside and does groan and creak a bit. I initially blamed the roofers who put on a new torchdown on my flat roof a few months ago, but they said the roof is "tight." Maybe the noise has always been there and I'm just more sensitive. As for weather, it's a pleasant SoCal sunny winter's day, with none of the extremes found elsewhere. So I don't think it's contraction/expansion. Pretty sure it's not a rodent, unless it's quite rhythmic and too lazy to move about.

    P.S. the noise is definitely not as intense as the sound captured in OP's post. We don't have AC either. At a guess, I would say a pipe is involved.

    1. Expert Member
      Zephyr7 | | #21

      Roof membranes flopping around shouldn't make a metallic banging sound, they'll make more of a "flop flop" sound. Hopefully that makes sense -- even though we have a phonetic alphabet, with letters describing sounds, it's remarkly difficult to explain a sound with words :-)

      I would check for any tree branches banging gutters or loose gutter sections, those can make noises in the wind, and maybe with thermal cycling too in extreme cases (although I've not see that myself). Pipe or duct sounds can be carried by the framing, so the actual source of the sound might be a distance away from where you are hearing it.

      You can check if it's pipes by running hot or cold water after it's not been run for a while. Pipe banging tends to happen when pipes either heat up or cool off quickly. Thermal-related pipe banging is usually a sort of "snap ... snap ... snap" sound that is periodic in nature, and gradually tapers off once the pipe has warmed up or cooled off all the way.

      Water hammer is a different sound, and happens at the time a valve is shut off. Water hammer is usually more a muffled "Bang!", sometimes with a rattle immediately afterwards as the pipe that went "bang!" bounces around for a bit (a second or two).


      1. MrFussy | | #22

        Thanks, Bill. I have ruled out the roof, and there are no trees or loose gutters. Pipe or duct sounds carried by the framing could be a good line of investigation. I'm definitely aware of pipe issues as my water heater is 16 years old - and it's the eternal question of should I replace it. We get a rumbling sound connected to my wife's shower usage, not to mine. I wouldn't liken it to a "snap ... snap" - and nor is there a muffled "Bang!" It's simply like a piece of metal or wood striking a pipe, and it's right in the bedroom wall next to where my head lies. Great!

        1. Expert Member
          Akos | | #23

          If you have cast iron drains it could be your drain stack or one of the vent lines. Lot of times the vent is run in interior walls, the roofer might have moved it enough during the re-roof that is touching some framing. Check if there is a stack vent on the roof in the area you hear the noise in.

        2. Expert Member
          Zephyr7 | | #25

          If you find a pipe rubbing on framing (such as the vent stack Akos mentioned), and you can't shift it enough to be clear, you can stick a piece of UHMW polyethylene sheet in between the pipe and whatever it's sliding against. UHMW polyethylene is a sort of linear bearing material, and it's great when you need something to act as a bearing between two things that are sliding against each other. Using a bearing material here is like lubricating the joint, and should eliminate the noise.

          Note that you need only a very thin sheet of the material to be effective. I'd probably use 1/32", or whatever was the closest standard size to that. You can even get it as an adhesive tape on rolls. I've used the tape-type UHMW to quiet down drawers that are wood-on-wood instead of real glides. Works great, and makes the drawers a lot easier to operate too.


  15. Roger Berry | | #24

    Mr. Fussy,

    A couple of long shot guesses for things to check. A loose vent screen for a crawl space opening if you have them or the flapper on a vent for bath or kitchen vent fan being sucked out and released by wind. This could account for the variable activity as wind direction would be a factor. A soffit vent with loose screws might do the same.

    Possibly a hot water pipe that passes through a joist or wall stud, which of course negates the wind part, though maybe the shower cycle is what is really driving the noise pattern.

    I did have one odd wind driven noise in a previous house. The mast pipe for the electrical wire hookup was bolted to the exterior wall of our bedroom. The top retaining clip was oversized for unknown reasons, so when the wind blew hard enough to make the service wires wiggle the sound of the mast pipe moving about in the bracket would transfer via the stud it was screwed into the bedroom. I remember it being more of a creaking and thumping sound.

    If you have a Casper mattress, it may just be ghosts.

  16. gibberishmock | | #26

    I know it's a old post but just curious...did you find out what that sound was. We are hearing similar sound in our wyze camera as well.

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