Grinding Sound coming from rear axle...

so i got an 06 chevy dually thats bagged. if i have the rear end lifted about 6" and cruise between 40 and 60 mph and let off the gas it makes a grinding sound. But accelerate and goes away, also if i lower the back end about three inches then it doesn't do it at all. I've checked ujoints and carrier bearing and everything is tight not worn. What are your opinions?

what kind of suspension in the rear 2 link 4 link?, could be bad pinion angle causing it

two link with bag over axle. where would the noise come from if it was the pinion angle? and only does it when the angle is in a certain position.

with a 2 link the pinion angle can become extreme , if its set up for a low ride height when you jack it way up it probably is putting the diff at a bad angle, maybe the noise is the u joint binding? if its normal just driving low i would have to guess its def. to do with the pinion angle. if it is you would be better off with a 4 link set up.... the pinion angle of a 4 link changes less throughout the suspension travel.... just my .02 good luck

I appreciate your input. It does make alot of sense what your saying so ill look into changing it into a four link. I just don't want to waste money trying to replace parts if it doesn't need it.