The whine goes away in neutral along with the rubbing/grinding noise.

 

Since all the noise goes away when you're in neutral means that all the noise comes from the "power" side of the gears when they're actually under load. If you're coasting along in neutral, the axles are driving the driveshaft (instead of the driveshaft driving the axles), so the gears are riding on the opposite side of the teeth than normal. All this does is verify that there's a gear problem IMO. "Proper" setup may or may not help.

 

So, there's no chance it could be the driveshaft?

 

I don't understand what you think the driveshaft is doing to make that noise? Hitting something?! How does a driveshaft make an intermittent "grinding noise"?! It's either always rubbing/hitting something, or never hitting anything. I mean, I suppose maybe a U-joint could be getting tight and binding up as you slow down, but I really doubt that, as I'm sure there would be a heck of a vibration in the car always if a U-joint was going bad. Gear noise is gear noise; JMO:blah:.

 

I certainly do appreciate everyone's replies to this matter. Thanks guys!

I'll just pull the diff again see if I can find something I missed.