The answer hasn't come yet, but if you used the old pinion bearings or if you have the pinion too tight you could get this noise. I have heard this noise when a person didn't use a new crush sleeve and put too much torque on the pinion nut. Old bearings should have 15 Inch lbs. to spin the pinion no ring gear installed, 18 to 22 inch lbs with new bearings, no ring gear installed.
Believe it or not i have used many gears from Quick performance, they are made in Italy by the same factory that makes many of the European gears. They cost $110.00 per set and i've installed them in everything from a 4.70 dragster to a 3500lb S/ST car and have never broke one yet (knock on wood) I not suggesting that you didn't check all these things mentioned, but it's just a thought.
Zip.