Diagnostic assistance request: rear suspension clunk

So I've replaced the whole rear end of the car on my own at this point. There aren't a lot of mysteries or variables going on back there which is why this is a bit perplexing.

So most often I'll hear this clunk when reversing and hitting the brakes to stop. It seems to emanate from the rear of the car, seemingly from the right rear though it's hard to tell. It also happens once in a while when I'm slowing to take a 90* turn, as the transmission downshifts. I suppose that it seems to be related to changing the direction of force on the drivetrain, not induced by hitting a bump.

It started after replacing 1.5" lowering blocks with 1" lowering blocks. It seems pretty consistent (not getting worse) after a few hundred miles...but something isn't right. I climbed under the car and checked all of the U-bolts. Everything seems tight.

The list of potentially relevant components:
A904 with a TF2 shift kit
Hotchkis leaf springs
Fox shocks (as prescribed by Hotchkis)
8 3/4" rear (Moser housing)
Eaton Trutrac helical differential
A recently installed pinion snubber...which is admittedly pretty close to the body when at rest, part of what prompted me to find another 1/2" of suspension travel.

Could this be related to the internals of the TruTrac? Could the axle be twisting enough to cause the snubber to knock against the floor? Does it even move that much? The noise seems maybe a bit harsher than what I would expect from the rubber snubber...and I don't hear when I hit bumps.

Any suggestions of what else to check would be welcome.