Why don't you remove the CV joint, and then remove the keeper that holds the bearing? Don't be too surprised if the bearing is completely shot, as you suspected.
This isn't the problem. Unless the diff is run completely out of oil the sidebearings will be fine. They hardly ever wear, let alone become "completely shot". The gears will fail from low fluid way before the bearings will.
As I said. The Bearing cup tightens or loosens the DIFF CARRIER side bearings. The diff bearing isn't the issue, it's the slop between the stubs, and the spiders they slip into INSIDE the diff carrier. There is no way to tighten this without replacing the spiders and stubs. Even brand new ones have a bit of wobble.
Properly done, there wouldn't be any harm in inspecting the bearings. PROPERLY DONE, is the key. Messing with the bearing cups without knowing what your doing, or without marking and reinstalling properly, is a quick way to ruin your ring & pinion.
To the OP......I'm telling ya, new axles commonly make noise. If you've got a reciept, I'd try taking it back and trading for another.
Edited by Gloyale, 04 May 2013 - 10:30 AM.