Click from rear end when backing up new 2500HD

[MikesZ06]

I test drove a 04 GMC 2500HD 6.0 yesterday. When backing up I noticed a click or clunk from the rear end after moving about 10 feet backwards. The truck did it repeatedly. The truck had 10 miles on it and a limited slip 4:10 rear end. Is this normal with the new limited slips? My current and past trucks never did it.

[more.power]

My 02 2500HD 6.0 did the same exact thing. Every day I would back out of my driveway (about 35ft) and turn left and cuuullunk. The dealer said it was the locking rear getting stuck and they changed the fluid. It cleared up after that. I ran it to 60k with no issues. I have since traded into an 04 DMax and I didn't have the issue with the new one.