New true-trac differential whine
Pinion Depth
Pull it out and check the pinion depth.
Get a picture of the wear pattern on the ring gear with the yellow marking grease.
Don't want them running near the toe or the heal of the ring gear.
Have to find out if they used the crushed sleeve eliminator kit. If it is a crush sleeve and they crushed it too deep, time for a redo. If it is eliminator sleeve just add another shim or take one out as needed.
Good Luck