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I've asked numerous people and no one has the slightest idea of what this can be. I'm hoping y'all can maybe come up with ideas to help figure this out.

I moved to the condo three months ago. For the past three months I've been using the heating and when sleeping in the master bedroom it's a very quiet environment. About two weeks ago I turned on the air-conditioner for about 10 minutes and shut it down on a warm day. When we went to sleep in the master bedroom there were loud crack noises coming from the ceiling and the walls around us. This went on from the time we went to bed all the way until we woke up around 11AM. I didn't turn on the AC for a while and it became silent in the master. Just the other night I tested it out again by turning on the FAN for about 5 minutes. Again, at night when we were trying to sleep, loud crack noises almost like you were lighting a firecracker or throwing a quarter against the ceiling.

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You're saying that noise occurs when the AC is running. Is it possible that your AC's refrigerant line runs through or above your bedroom ceiling? If improperly installed, it may rub against structure when the line expands/contracts as its temperature changes, creating the noise.

It's also possible that a noise could come from air ducts in your ceiling/walls, but from your description the most likely culprit is thermal expansion/contraction of a metal pipe/tube rubbing against wood.

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  • Shimon Rura, Thank you so much. This makes so much sense. I know that I'm using really old fiberglass duct work and some of it is a bit disconnected. I forgot to mention this in the question. I am wondering if I just turn on the units FAN, would that also cause the refrigerant line to do this? Any recommendations on how they can lay the ductwork so it's not sitting on the wood in the attic? – Philoxopher Feb 26 '16 at 22:45
  • Shimon Rura, You said "that noise occurs whens the AC is running". This actually happens when you turn the unit on for 5 to 10 minutes. Then about 3 to 4 hours later the noise is occurring when were trying to sleep all the way until morning time. All while the unit is off. – Philoxopher Feb 26 '16 at 22:47
  • It could be the line expanding when the AC starts up, then contracting when it shuts off. But for it to last several hours is too long unless you have a programmable thermostat or something that would turn it back on at that point. Mysterious... – Shimon Rura Feb 27 '16 at 13:44
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I'd agree with Shimon Rura & it's a common condition of holes drilled too tight to piping. But, I think just operating the fan & getting the same result that it's something else altogether.

Not to be an alarmist, since there's no apparent spread of evidence. But, get an HVAC guy or firm out ASAP. As, the only other thing that would make noises like that with everything either off or waiting to be called on by the thermostat is a very bad electrical problem.

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