[f5fstop]

Ok, you guys got me, in the past two days, I have noticed this groaning from the left rear brake; not a grinding, but more of a groaning when coming to a stop under heavy pressure. Slow stopping does not bring on the noise, only heavy or very heavy.
At this point I am not sure what it is, but it is not due to a warped rotor, this was confirmed today.
Personally, I'm leaning toward the inside the rotor's hat park brake assembly, and the brake shoes rotating on a dry backing plate. (L-Series Saturns had the same rear park brake system, and the same type of groaning noise; not as loud, but similar.) In other words, the park brake shoes are hanging up. This could explain why the rotor is removed and turned and reinstalled, the noise goes away due to the freeing up of the park brake assembly when the rotor is removed.
If it is the park brake, it would not cause a braking problem, only an aggravating noise problem.
I am trying to schedule the H3 brake service engineer to come over to my facility and let's tear into this and figure out exactly what it is.
This will take a few days, but I'll keep you informed.