Heat pump indoor unit makes frequent but intermittent clicks and thunks

afriedl

A little under a year ago, I had 6 Carrier mini-splits installed, with two outdoor units. All of the indoor units make intermittent clicking/banging sounds, which are frequently loud enough to startle me awake as I'm falling asleep and occasionally loud enough to wake me from a sound sleep, even though I sleep with earplugs in.

These noises happen whether the units are in heating or cooling mode, and sometimes continue after the units are switched off and the fans are off (and the pump should be too, although I don't know that for certain.) They're not a result of the louver/vane moving, since they occur when I don't have the unit in "swing" mode. They occur on two different systems with no connection between them, and on several units that are on an outside wall and one unit that isn't.

It's difficult to get recordings since the problem comes and goes, but here are two:
Several moderately loud clacks
One loud thunk, followed by quiet and then two quieter clicks

The fact that the noises continue when the units are off makes me suspect something related to thermal expansion and contraction; is that possible? My installer seems to have no idea what it could be. Thanks, all.

Jamie Hall

Probably expansion/contraction -- but where in the unit I wouldn't have a clue. But if that is quiet in between, I'm very glad I have steam heat...

afriedl

I placed the mic directly on the unit and normalized the recording volume; from even a few feet the fan volume is quite reasonable. Thanks!