Rearend noise

It's probably pinion preload, or lack of it. What you are hearing is the early stages of self destruct mode. Once the pinion is allowed to run misaligned the gear set is pretty much garbage. If you replace the pinion bearings and set the preload correctly you might (and it's a big maybe) get an acceptable pattern and reasonable lash. They will most likely still be a little noisy. Once gears get noisy the only way to make them quiet is new gears. As others have said, the pinion can hit the carrier. This just fills the axle housing with shrapnel that will destroy everything in short order. I just spent 2 hours under a Chevy truck cleaning the metal gunk out of a 12-bolt housing because this happened.