I noticed that a couple of my ceiling nails were extruding about 1/8 inch, and grabbed a step stool to investigate. I pushed up on the ceiling, and there was about a 1/4 inch gap between the ceiling panel, and whatever is behind it. I tried to tap the nails back in, but they would not hold. I tried a slightly longer and larger nail, and hit something solid! I'm guessing that it was one of the aluminum roof trusses. What exactly is behind the ceiling panels. Is it plywood. If so, I can just re-position the nails so that they don't hit the trusses!