2003 Nissan Frontier Wierd Noise

I have a 2003 Nissan Frontier Crew Cab. 3.3 V6 with 123,000 on the clock. I have a noise/vibration that begins at 35-40 mph. The noise sounds like a wheel bearing, however upon lifting the front end both wheels turn smooth and free. Also the noise gets a deeper/louder tone upon accelearting, especially when going up hill and is accompanied by a vibration. But below 35-40 you cant hear the niose..????