Help... Noisy 12 bolt

[carbondaddy]

First a little history. 69 Camaro 12 bolt posi. It had 3.90 gears which were too much so I had a shop install 3.07's until I can afford a 5 or 6 speed. While it was apart, we found that it had suffered some trauma in the past. The carrier had pretty deep gashes from what looks like the pinion gear. He measured the runout on the ring gear and it was within 1 thou, so he thought it was OK and finished up with the change over. Ever since, the rear end is very noisy under light acceleration and steady cruising. I've had it back in the same shop 3 times and had another mechanic look at it. Each time they say it is within specs (I don't know too much #'s). Any ideas? The carrier hooped, the replacement gear set not good? I didn't notice the 3.90's being noisy, but the rest of the car was very loud. Maybe it's just time to spring for the overdrive tranny and put the 3.90's make in.