Loose diff
 

Fitted new Ceramic diff balls and Thrust balls today,(buds balls) tightened the diff screw up and heard a crack and one of the thrust balls had smashed,and when I tighten the diff up it works itself loose when you turn the diff,I don't think I was being ham fisted with it!!

I had this once..

Rebuild your diff again, check if all the parts are still good, if nothing is worn out etc

problem I had was something with te spring. I'v putted it in the wrong side..