So I just recently replaced my rear axles/hubs with the Z1 370Z/G37 kit (and then further had to get the Kawasaki Castle Nut/Torqen-style cotter pin and washer kit because the stock Nissan aluminum "hat" nuts are garbage, and I thought the click was that at the time). Hubs were on the way out and I saw an opportunity to upgrade/get beefier parts.

HOWEVER, my original (2005 5AT Coupe) axles/hubs had the infamous click/rattle, which did go away with the new parts...except I now have a new click whenever I let off the throttle (can't hear it when I go onto throttle). It's a fairly loud (can hear it with the windows down on an open street, but not with the windows up), single click/tap, sounding like metal-on-metal...but I'm at a total loss. New hubs, new axles, everything torqued to spec, Blue loctite, can still hear it with the brakes lightly pressed at lower speeds (to try to rule out pads moving around), new parking brake hardware on both sides...with my OG axles/hubs the click was just when going from Park into Drive/Reverse, but this is 90% of the time I let off throttle. Started when I did axles/hubs (I'm 90% certain, unless it's the same one from before the axles/hubs but it was masked by the hub noise back then), but I've double-checked every fastener and new piece of hardware.

Aftermarket stuff back there is sways, GK Tech differential brace, wheels, parking brake hardware (and Les Schwab calipers/brake hardware, but they all seem fine); I'm inclined think think it's something in the driveline either where the driveshaft connects to the differential (or further downstream), but I've spent so long chasing this down that I'm going nuts. Axle splines were coated in copper grease when installing.

I did manage to trace it (I think) to somewhere between the differential/wheel when in Park/engine off by pushing the car forward/backwards gently; I got a single click, and then it refused to make the sound again, making me think it's something in the driveline that works loose, clicks and becomes "secure" when I go off throttle, and repeats. I also heard it when coasting off-throttle in the garage, and the passenger-rear wheel went over a small bump. The vehicle has new Tein Flex on it, but again, I've triple-checked all torque specs, and it makes no noise in all other cases.

And to clarify, torque spec for the axle nut of a 370Z should be 75 ft/lbs, yes? I've seen some people with the same hardware do all the way up to 130 ft/lbs, but I was going by the torque specs Z1 quoted/the FSM says.

Anyone have any pointers? I'm going nuts trying to track this down.