How do you tell if you posi or rearend is going bad?

I have a 96z mostly stock just catback and cai. A4 been to the track twice RR, once to autocross. I only have 41000 miles and this is mostly hwy miles.

My problem is if I make a tight turn, usually to the left, I hear a lot of groaning and moaning noises form the read. Is it time for a new unit or ?

I've change rear fluid 3 times, the first time I listed to the shop and let them do it, they said they used synthetic so I didn’t need posi additive. Two months later I got nervious and changed it the day before a open track day and added posi lube. I didn’t hear any noise but about 6 months ago I changed had it changed at the dealership and now I starting to hear noises.

Advice? Should I just add more posi additive? Or ????

Thanks

Jon
96Z