After reading previous posts on this thread. It would appear that the noise is the result of poorly finished bevel gears.

While not being an engineer, all comments here would seem to point the bevel box being pushed into service long before the gears have been mated.

What solutions are there?
Professional lapping service has been mentioned, but at what cost?
A less protective oil to aid "running in".

Running in, that’s a thing i`ve not heard of for years.

Would it be feasible to get this done by Quaife? Lets say, for a small fee.
So that when(the bevel box)is fitted its sorted.

After all, it would be a lot more expedient and cheaper to do this before fitting than swap them out later.