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.