Wow, went to start a new thread checking for fix for klunk w/I saw this.
I have '88 turbo s/w f/t 4wd. Klunk from rear on hard accell. after driveline unloaded. Replaced axles. u-joints good. Diff mount appears ok as well as "moustache" bracket bushings. Removed arms-all bushings still good thoughthey show rust from rubbing!?
Feels like excessive differential slop as alluded to in last post. Would hate to think only cure is replacement but...
Still looking at answers, will post as I try different things. Local Subaru shop says they have never been able to fix one yet!? : (
Thanks for a great site! JEFF