First thing I would check would be idler gear teeth and any gear inside of it, look for chips or rounded off teeth. If the look find and you are running the ball diff I would open it up and assure that all of the balls are in place, maybe one could have jarred itself loose and is rolling around in there.

That is where I would start personally, and mind you I don't know if this is a known AE issue I am new to the brand, I would do this on ANY car that had a clicking noise in the tranny.