well as it says, when my car is at idle sitting in the driveway I hear this noise its almost like a short grinding/rubbing noise. I also notice it when at redlights etc. It sound like it may be coming from the differential, the car has 51k on it and I am planning on changing the fluid back there with some mobil synthetic and some gm additve soon. Any other suggestions or ideas?

 

When the car is sitting still idling, there's nothing moving in the rear end (unless you're bouncing the suspension up and down), so I don't think your differential diagnosis is correct. I'd more likely point at the clutch throw-out bearing, known to rattle at idle. That's pretty normal. You could also put it up on jacks and climb under there while it's idling, to see if you can pinpoint the noise more closely.

Dave

 

hrmm....good idea I will stop by my mechanics and put it on the lift and see if we can deciede where the noise is coming from, I was also think maybe the exhaust pipe if hitting some part of the car. causeing that noise.