Seeking some advice on what could be causing a grinding noise in my drivetrain (Land Rover Series IIa, 2.3P, SWB ).

The grinding noise is only noticeable under no load situations at the neutral point between acceleration and deceleration. As soon as a load is placed on the transmission all is fine.

I only hear the noise at higher speeds (when switching between 3-4 gear).

Made a video that clearly illustrates the noise. Noise starts at 7th second.
Land Rover series iia noise during deceleration (overrun) - YouTube

I replaced the UJ’s and had the propshafts rebalanced.

Took the gear and transfer box out (main shaft brass distance bush was broken), double checked all end floats and other green bible specs.
Took the rear differential apart: end float of ring gear and the gear contact pattern seemed fine.
But still hear this noise ☹

Any help/guidance would be very welcome! thanks!