Sorry to say...
Sorry guys. This was the first major thing I looked into when after buying my '05.
This condition is on all the GTO's (and apparently the C6 'vettes to, so I'm told).
I'll look for the thread I read somewhere that explains it in detail, but it is normal operation, unfortunately. Has to do with the *Parking* brake (notice I no longer call it an e-brake) is built into the inner diameter of the rear rotor, and when energized, it clunks majorly on the inner wall if the car is moving.
Why they would put a system like that on a performance car with a HAND activated parking brake is beyond me. But that's just the way it is. Nothing's broken or misaligned...