I hava a moser 12 boolt w/ 4.10s in my 02 ss and my rear is making an awful grinding sound, usually for a few seconds after i let off the throttle. i brought it to the shop where i got my h/c installed and they said that it's nothing to be concerned about. is this true or is it a matter of time until the rear blows. if it is a problem, would it be able to cause any harm to my transmission?

 

This doesn't sound correct to me. There should be no grinding noises at all. Try bringing the car to someone else to get a second opinion. Good Luck.