probably that auto locker man, is this rearend new to you? is it only when turning? what speeds?

 

This is my first time with lockers but I know how they click etc around corners, this just seems like it is happening on the floor of the rear cargo area. That's why I'm thinking it's at some connection point for the suspension/axle.

It happens at slower hard turns, roughly 5-15 mph.

 

Since you have a locker, I would suggest testing it to rule it out if it's not the cause. Jack the rear axle off the ground and have a buddy help you rotate the tires to force the locker to differentiate. If you can't get it to or it's making an excessive amount of noise that might be a problem. Sound waves to odd things. I have an exhaust drone in the back that you can't hear outside the vehicle... something with the resonance of the rear floor and my new exhaust system.

You would think it would be obvious, but did you put oil in the axle when you put it in? I had a co-worker that is a hard-core off-roader that forgot to put the oil in in the process of putting a D60 or something in his Bronco and it didn't fair so well, as in pretty much exploded. He didn't have to rip it apart before install and the other co-worker who sold it to him never put oil in after rebuilding it out of vehicle.