When I accelerate lightly there is a clicking noise that seems to be coming from the right rear axle/tire area after it shifts from 1st to 2nd gear.

It only happens when I accelerate lightly. Can't hear it under half throttle or more. I know this is little to go off of but I am looking for any thoughts.

I just installed 2" Lowering Shackles last week, installed to spec torque and everything.

2006 Chevy Crew Cab, 5.3L, 3.23 Locking Diff...thoughts?