The axle is the inner race of the wheel bearing on c-clip style rear ends. It seems that the 7.625 10 bolt rearends in our vans have a history of issues with the hard surface on the axle flaking off. Once this starts, they get noisy quickly. If the noise goes away in a right had turn, the bad bearing is on the right side. Turning takes the load off the inside tires/bearing/axle, and usually the noise while go almost completely while tuning. I've had issue with this once, and my brother has twice(second time was a new GM axle that failed almost instantly. Both of us repaired ours successfully with junkyard axles and new bearings and seals. You need to pull the axle, inspect the race surface, if any pitting is present, replace the axle, bearing, and seal. Another note is that this sometimes start with a low fluid level caused by a bad pinion seal.
It's not a hard job, but it smells like crap and requires some specialty tools (bearing pull and seal/bearing driver). A full set of seal drivers is about $20 from Harbor Freight and the puller can be rented for free from Autozone. I use brakeclean and compressed air to clean out the housing. I never use a gasket on diff covers, only black or orange RTV silicone. The 7.625 has a drain slot in the housing that goes almost to the edge of the cover, so you do need to be careful that the silicone goes beyond this slot.
Here's a pretty good video showing how to get the axles out.