When I shift into reverse there is still a clunk and a pcasional grind. Its a auto. Doesnt seem that is coming from the trans or t-case. But who knows. Anyone ever have a simalar issue with a xj? I did replace the u joints yesterday in hopes of solving this. Also when I let off the gas going normal forward speed I hear a clunk too. Gos this is getting me.

 

Check your pinion nut.
It might be loose and allowing the pinion gear to move in and out.

 

I cant see some movement when im under it but ofcourse it doesnt make the clunk when im under the damn thing. I have been told maybe the tranny mount but who knows now

 

Mine clunked when my transmission mount was loose.