4 Wheel Drive/SUVs: binding in 4 whell drive, wheel bearings, ford exp

Question
I have a 99 ford exp. eddie bauer and when i go up a hill or increase my speed (especially on a highway) i get a binding noise in the front passenger side ... then if you put it in 4 wheel high or low once you begin to speed up to around 15 mph the binding noise starts again, it is worse when you turn the vehicle left or right.... have already changed the differential made it a little better.... have heard from some other it could be the shift motor, transfer case-, even the u joints... please help ..  

Answer
Have you tryed replacing the wheel bearings? If not I'd replace them on all 4 tires.
If it was a U Joint you'd hear more of a clunking sound. I know I've heard of the same noise being made with chevys in the right front(passanger side) and it too was the wheel bearings.