I've had the same noise (sounds like rear bearing). The car is a 2001 with only 31,000 miles on it. I thought about checking or changing the rear bearings, but I just can't believe they would be bad at that mileage. So I'm hoping it's maybe just a camaro thing. It doesn't seem to be getting louder so I'm just going to keep driving it, I'll leave a post on here if something does give out. Barb.

 

That growling noise never really got worse for me either, but I can assure you that it is the diff. bearings. Its not about age per say, but instead whether or not the rear differential was put together bad, which if it was, causes too much pressure on the bearings causing them to go bad. I wouldn't advise driving on it too long.... if it gets bad enough it might cause your whole diff. to get messed up.