rear diff/propshaft clanking/banging at low speed

[Uzelac]

I have some unsual noise in rear end, diff assembly.
Diff is TRD 2way, new with some 2000-3000 km. Whole rear end was rebuilt with new bearings and stuff.

Sometimes, when driving slow i here not so loud metal bang/clang noise.
It's connected with changing load on rear end, when i cut off power or push throttle, or press/release clutch. It doesn't happen allways, sometimes, like once in every 10 times i repeat this stuff.

Sounds like something hitting a metal, not loud.
My car doesn't have rear seats nor any dampening material, and the level of noise isn't loud. Level like normal knocking on wood ...

Diff looks to be ok, it' works ok, there is standard whining at 80+ km/h but i believe it's normal. When we rebuild it, CWP was looking good.

It could be propshaft olso, maybe some connection has too much foreplay ?

Anyway, where to look, and should i be worried ?

Thanks