C6 Rear end noise...

I have a 2005 C6 Coupe (auto trans) with about 18k miles. Car has developed a chatter in the rear end when turning at slow speeds - worse in reverse but will sometimes do it going forward in a tight turn at slow speeds. Took it to the dealer and they added some anti-foaming fluid to the rear end. Service guy aid it was clutch chatter. Keep having to have this done about every 6k miles. Anyone else experience this? Same solution?

Thanks!