I thought that the bevel gearbox gears are straight cut, hence all the noise. This looks like helical gears to me, a crown wheel and pinion, like mosts diffs. They ususally make noises because of incorrect preload or worn bearings. Nice to see the insides. Also be interested in the reason for the strip of the gearbox.
I had also understood that the bevel bow used straight cut gears. The NVH mod make much more sense with helically cut gears. The splines on the input/pinion shaft don't look to be in very good shape though.
