2014 Sierra LOUD noise on decel.

[HooWybrow]

Hey guys, I've got a 2014 GMC Sierra SLT, 6.2L, 4wd. It is lowered 5/7 currently. If I'm driving on the highway, anything above 80km/h (55mph+ I think) and coast, I get a horrible groan type noise from the rear end. Only when decelerating at that speed or higher. The second I blip the throttle it's gone. Anyone else get this?

[fondupot]

pinion angle? you said you are lowered, maybe the lowering kit is causing a bad pinion angle and causing a binding of the drive-shaft and that is what you are hearing.

[HooWybrow]

Pinion angle could not be any closer to what it is factory. It has been shimmed appropriately. I feel like it may be in the gears? Not sure.

[20L8TSierra24]

With it lowered, the dealer might give you trouble.. Might want to put it back to stock if you take it in. It might be the leafs popping like others have had.

[HooWybrow]

With it lowered, the dealer might give you trouble.. Might want to put it back to stock if you take it in. It might be the leafs popping like others have had.

 

I'm a licensed tech at the dealer, warranty really isn't an issue, hahaha. We've been hunting this noise for a little while and I figured I'd ask if anyone has run into a similar issue.

 

Update: I've found a very possible source of the noise. Rolled the truck onto the hoist after work and checked things out for what seems like the 300th time. I believe the front u-joint of the rear drive shaft has some issues. It appears the u-joint caps in the actual driveshaft are spinning in the driveshaft, the caps are polished (both caps in the driveshaft) as if someone has been buffing them with emery cloth. You can also see where the retaining clips have been scoring the outside of the cap as it rotates. I marked the caps location tonight and am going to take it for a good "after hours diagnosis drive" tonight. I'll let you guys know how things work out tomorrow.