Occasional clunk from T-case going in reverse

[EB4X]

As title states.....on a couple of mild off-road fun excursions I experienced a couple reverse clunks (coming from transfer/tranni area) going into reverse while in 4x4 mode (only happened in 4x4 mode....not 2wd) ..... Happened on two outings ....one time each....and went into reverse about 5 times each outing...
Any suggestions on what I'm dealing with specifically.....

 

[Mbrooks420]

Was it in 4wd high? Are you sure you weren’t winding the driveline up? The rear driveshaft slip yoke can cause a clunking in reverse when it dries out. I’d crawl under and check out the u joints for play to start.

 

[Stic-o]

U-joints