trd offroad 8 3/4'' rear axle manufacture

I like to know what /who manufactures the rear axles for Toyota for the trd locking rear axle .. why are so many of theses axles noise between 45 mph to appox 60- 65 mph, I am on # 2 replacement but the truck is out of warranty,, it seems like it take appox 6000to 8000 miles to show with noise concerts .. I was a tech for Toyota for 26 years (out of the industry) never saw so many complaints on rear diff when at Toyota, is the a problem setting up the rear Dif's or manufacture problem with gear set... its like hit miss if you get one that that's not going to be noisy