Cass, a.k.a Dr Diff has always told me to use the Ford Racing Friction modifier. Add at least one bottle, and use 2 if you still get differential chatter. My local rear end shop recommends the same claiming that even though most dinosaur and synthetic gear oils are being produced with their own friction modifier these days.

The clutches in my Dana 60 started to chatter on turns after a while and I added a second bottle. It stopped it again.