So I am getting a grinding noise out of my suburban. It happens when accelerating after hitting a bump or dip in the road.

Details- Mostly at lower speeds. I've never heard it on the freeway or anytime cruising.

It happens after things warm up. Almost never when it is cold.

There is not a loss of power and the noise stops quickly if I let off the accelerator.

It is a harsh sound like gears grinding or a metal on metal rub.

I did check the differential fluid and it is full and the fluid looks clean. I believe this vehicle has the posi-traction rear end so I don't know if the previous owner changed the fluid and did not put in the posi-traction modifier???

It will make the noise when going straight, and/or turning left/right. Going over a bump is almost always the cause of the noise.

I honestly can't tell if it is coming from the front or the back of the vehicle. We have had it up and the lift and the driveshafts and u-joints look fine.

Any suggestion?