I heard an old mechanics tale of sandblasting the R&P and set it up again. The guy said it allows the R&P to 'mate up' again, then you readjust after 200 miles. Could be a load of stinking carrier lube, I dont know.
I used to sandblast ring and pinion and then set them up.
Had a mechanic tell me that sandblasting them changes the hardness of the gears. And I thought about it and I stopped doing the sandblasting.
So I don't know. I don't remember having a whine on the ones that I sandblasted though.