Corvette, rear end noise

I have a '79 Corvette. My mechanic said the car was mechanicly solid. No problems with bearings, U-joints, brakes, engine, etc. But, I do seem to have a problem. If I drive the car for 20 to 30 min. whenever I get to my destination, the rear end will groan and give a slow low squeek, like and old castle door in the movies. I asked a friend of mine, who is a mechanic for an exclusive Exotic Car dealership (because my other shop was closed) and he said that the brakes could not be releasing all the way and getting hot, thus causing the noise at trips end. When my shop reopened on Mon. I called and they said it was possible and that he knew it wasn't any of the bearings 'cause he checked very closely on Fri. when it was on the rack. If anyone can help with some info before I start tearing her down I would be very greatful.