I’ve had a noise coming from my rear end since I got the car and usually it stayed consistently bad. A year or more ago (I barely ever drive this car) I had the fluid changed in the differential, and that made the noise significantly better barely noticeable at all. Now, however, the noise is back and seemingly worse than ever. It’s a low pitched grumbling noise almost a grinding and really only does it when I reverse or am turning one way or the other. Since this is such a high performance car, I’m worried the rear end is just going to blow out on me one day. Can anyone tell me what might be going on and what’s causing the noise? Also, there’s no play In the drive shaft for it to be a U-joint or anything
Please let us know what make, model, year and what equipment is on this HIGH PEREFORMANCE car.
I’ve had GM cars with limited slip differentials and they are sensitive to having the exact fluid and need it changed every 12,500 miles.
Oh I apologize I thought it included it in here (first time user). It’s a 2005 Pontiac GTO with a 6.0 L LS2 engine and a T-56 6 speed manual transmission
You may have damaged the clutches in the rear diff by running it so long with the noise prior to changing the fluid. I’d suggest removing the cover for a look-see assuming you know what to look for 
BTW- there’s a board dedicated to this generation of GTO- http://www.ls1gto.com
Ok thank you. And if it has any relevance, I’ve only put about 1,000 miles on this car in the last 4-5 years so it doesn’t move much