Crack! Body Panels

Weird Question (what other kind?) I have an 87 GT, I bought it new and 240000 miles on it, lately I am getting a loud Crack! sound overhead somewhere around the sunroof area on rough roads. I have at the same time developed a small (1 inch) semicircular crack over the drivers head in the rear roof panel. Anybody got any idea what is going on under the plastic?

Sounds like the studs (molded into the plastic) that hold the panel on are breaking loose.