Rear End problem again WTF? Making a noise

I have a Auburn locker and a set of 3.73's in the back. When I drive it sounds like Iam dragging a chain at any speed I dont know what it is. Do you guys think I broke some thing in the back. I talked to the shop and they told me to bring it back by. The car has less than 250miles on it because 3 weeks later the tranny let go on me. SO the car was down the hole month of July.
 
mine makes a racket but only when i back up real slow after its all nice and hot from spinning so fast. sounds like it might be the wrong frictin additive. since auburn is a GM diff. it requires the GM friction additive, the ford will lock it up real tight and it will make lots of noise.