If it's not in the U-joint;
Ima thinking there might a tooth or more broke off the spider gears.
The other thing that happens is the cross-pin saddles "waller" out. Then you get a clunk going into gear, and also from forward to reverse.
But that clunk, is hard to differentiate from spider-gear endplay.
In any case if the clunk originates inside the diff, it has to come down.
