My 2001 Z 28 has a hair under 47K on it. It has the stock rear end with the 3.23:1 rear end ratio (GU5). I start getting a whine at low speed that increases but I can't tell if it's from the center or right rear wheel. I don't think it's ring gear / pinion noise as it does not go away when I take my foot off the gas pedal. vehicle is not driven hard. Pinion shaft seal was replaced by dealer at 30K but everything seemed ok.
Anyone has any ideas or similar experience? I also need help finding instructions on rear end set-up in case I decide to take it apart. Thanx.

 

It could be that you have a bad rear axel or rear wheel bearing.

 

I state this because I recently purchased a 1997 Z and it had a bad rear axel, so it was loud.