I recently bought a house with Daikin mini split units on the second floor to provide heating and cooling – the unit in the bedroom will randomly buzz for a second or two at a time and it can repeat every 10 seconds or so for a few minutes, then stop for a while – it even continues to do it when the unit is powered off –  i recently had to have the freon refilled and recharged but otherwise it seems to be working fine – is it a problem with a water pump that removes moisture from the air?  the unit in the bathroom does not do that sound so i’m assuming its something that needs repair or replacement