Is it shuddering when you're making slow turns? Try changing the diff fluid. That usually works.

No shuddering at all, and the rear diff fluid was changed 6000 miles ago. I tried slow/high speed turns at a large parking lot but still couldn't find the problem. However, I just found I can also hear the noise sometimes when driving straight on the highway, it seemed pretty random.
I don't know if it's related but my wheel studs were stripped last month. Car was towed to a local performance tuning shop. They changed the front/rear studs but for the rear they had their machine shop rebuilt my old hub with new bearing. Is it possible that the hub is getting loose?

I see. Unfortunately I have no experience on that man, sorry :( maybe another member could help.