I wonder if your motor mounts might be shot. Not to keep throwing ideas out there but mounts are hard to tell visibly if they are bad and they do cause clunking sounds from the engine moving when their shot. Maybe something else to double check if they have not already. It does suck to get the runaround. Hopefully they find the issue.

 

Lavrishevo.
Supposedly the motor mounts have been checked. I don't know how carefully.
Yesterday I met with the local "Senior Diagnostic Technician." He has heard the noise in the past. He does not have a clue what it is and refuses to consider the driveshaft spline as a possibility. He feels that it is a normal transmission noise even though he has never heard it on any other 8 speed. His recommendation is to monitor it and let them know if it gets worse. Bottom line, I have to live with it. Not pleased at all.