Whine in the rear end

[BigPoser]

Working on getting my truck driving properly and I'm getting a sort of whine in the rear end. I changed the fluid in the diff thinking that it may have been low, which it was. Truck sat for a good two years before I got my hands on it. Still whines a bit after the fluid change.

Could it be the bearings? Something else possibly? The gears within the diff looked good, and there were no shaving of any kind either.

Thoughts?

Thanks in advance.

Brandon