Thanks for your quick replies. I have never heard the noise. The owners say they are sharp cracking sounds. I have photo'd and noted the timber checking over the years, and the timbers checks are not getting bigger, and I don't notice any new ones.
panels were 4" wall, 6.5" roof, polyurethane & OSB. Big panels, 8'x16'-21'
The owners did say they thought there were a lot of panel screws left over when the job was finished.