1SWT95Z

I am hearing a defined noise coming from the rear of my 1995 LT1 camaro. The 3.73s I've had in it since 2003-2004 have always made noise on coast and very slight on accelerate. The new noise started Saturday and shows up from a rolling start, sounds like a low growling version of gear howl and is heard until about 10-12 mph in first gear (auto trans, stock stall), goes away in 2nd, and 3rd and shows back up in 4th(OD) 40-50 mph. Today while driving it seemed to coincide with the normal rear gear noise I am used to hearing meaning accel and coast. I guess I need to know if any of the bearings or the posi trac in the rear end were starting to fail, what would the symptoms be? Can the ring and pinion all of a sudden have more or less backlash and thats causing the new sound? I've checked the fluid level in the rear but have not removed the cover for inspection. I've also jacked the rear of the car up from the center and put it in neutral and rolled the wheels by hand. I can hear noise in both the rear end and transmission pan/torque converter area but I don't know how much noise is too much and considered a problem? What should I be looking for? Thanks