2000 Yukon front end noise?

[drywaller]

At first I thought it was the front hub so I changed it out. Still there. I have ruled out the brakes and am now thinking that it is the front end.
It is not the typical ring and pinion whine that I have read about here. It starts about 10mph then gets louder that faster I go. If I engage four wheel drive it goes away.
The only way I know of describing it is that it sounds like a wheel bearing going out. it is more of a osccilating sound.
Any thoughts?