Hi Fritz,

You might want to ask him if he has had wood crown molding installed within the last year, specifically more recently if this just started happening. I have heard on two different occasions with two different homes, that the owners would get a 'cracking' or 'pop' noise occasionaly (during dawn and dusk times); and both instances where the crown molding was nailed to the wall framing and installed 'too tight' (cut a wee bit too long and jammed into the corner mitre cuts), and this resulted in the noise from expansion and contraction early on after the installation, then seemed to go away after time.

Hope this helps,

Steve Lottatore