Did they preload the carrier?
Any used bearings used?
Defective Detroit?
Heres a good one, did they re-add some gear oil (!) ?
I think its all a shot in the dark, but good luck.
What about backlash? Was it built to tight?
You say they are professionals; Have you had other diffs setup by them without any problems? What do they say when you bring it back in and claim its making noise. Any good shop will tear into it and fix it since the noise was not there before they installed your locker.
Let us know what you find out,
Cya,
Mike
