Well Harry, the first thing I noticed is you are driving on the wrong side of the road. Just kidding. If I had to go out on a limb, I would say that the noise is coming from the mating of the gears. Just my opinion. I don't know why some gears seem to make noise. I had a 1983 Mustang, 7.5" rear. Backing out of the garage slowly, the car came to an abrupt stop. Pulled it back in, took it apart and a spider gear tooth had broken off and had somehow gotten between the ring and pinion and that's why the abrupt stop. Not much really noticeable on the ring an pinion.
I bought a new Ford posi unit and installed it. No problem, set the backlash. I never got the whine out of that rear end. I even paid a "expert" and same result.
I thought I remember someone recently having problems with a rear end with Motive gears?
Personally, I like Richmond gears. They come from the factory with the pinion depth and backlash scribed on the gears, of the setup dimensions used at the factory to run the gears in. I set them up to those dimensions and have never had a problem.
I am not saying to run out and change your gears, but if you are pulling your hair out trying to figure it out and you are throwing out money chasing this, it may be worth your while to install a different brand of gear.
Just thinking of this, you may want to check the drag on the pinion bearings to see if the gears were set up too tight as far as the pinion bearings. Just a thought.