I have the same problem with my SDW
I m hoping that with a new graphite gear (better fit and finish) and some carbide ball its going to disapear
Make sure when you tighten the diff to do it progressevely, dont tighten it in 1 go, turn the diff a few times then carry on tightening it till its like you want
This will help to avoid building your diff out of round
Forgot: Shim your diff in order to have your gear a little more away from the bevel gear, the whole diff should have some play