What exactly does gear noise sound like?

[LongrangeLauber]

First off, let me say that I will get this noise checked out, just figured to see if anyone here has any experience with this.

 

So got my truck back from the dealer today after getting the alignment and I really started to listen for any odd noises now that the tires weren't making noises and figured I'd be really aware of any noise coming from the freshly built differentials. Well the rear sounds fine, at least, I cant hear it, so figured it should be fine.

 

But driving down the road, any speed above 20mph I get a deep "whirring" sound almost like bearings (metal on metal) with no grease or oil of any kind in/on them. Ive checked the fluid I don't know how many times, front and rear, to make sure they were at the proper level, especially since Im breaking them in and don't want em to get to hot.

 

I don't think this has anything to do with the new lift, but it just worries me that the diff. could give out and I'll be out quite a pretty penny. Im just wondering if this is normal for aftermarket gears.

 

Oh, the gears are Yukon brand 4.88's, the rear has a Yukon Grizzly locker, the front is just the stock open diff, and there are new bearings all around in both the front and rear