So my 71 is finally back on the road after 38 years. In the 80's - I bought new 4.10 gears and a used gm posi unit.I had it professionally installed into the original rear end back then. Before I drove it - I put fresh gear oil and additive in. After 800 miles (yesterday) there is a whine coming from the from the drive line that gets louder with speed and throttle. It sure sounds like the ring and pinion but it may be the outer axle bearings. I do think they were replaced but i'm not positive. I bought some prussian blue, opened it up and checked the gear mesh pattern. Both sides look good. Centered between the face and flank (top and bottom). After inspection, there is quite a bit of play in the small spider gears - up/down 3/16". These do not turn when going straight so I doubt they can cause the whine. Could bad outer axle bearings make noise only under acceleration? It gets loud over 50 mph. There is also a slight noise on decel. I think its coming from the rear, I hope it's not the trans tail shaft bearing. Going to put it back together now as the ring and pinion seem OK. I need more test rides to diagnose noise. Just went for another ride.. i'm bummin' I think its the transmission. Maybe the tail shaft bearing? Cornering has no effect on the noise at all. Off throttle - quiet. slightly on the gas = loud gear whine. The gear I am in has no effect - noise is all drive shaft (and back) speed related. I checked the u-joints and they seem fine and are new last month. It's a BW t56 from a 94 Camaro that was supposed to be low miles (purchased in the late 90's). I'm going to check the fluid but I did recently and it's not leaking. Possible a tail shaft bearing in the trans?