97 Humming and Vibrating

I have a 97 Bravada that I bought in 1998. Its been babied. Now I got a vibration that starts to be noticeable at about 40mph and at 65 ot 70 mph the vibration lessens but you hear a humming noise. Took it to the dealer and at first they said it was a combination of the front axle and transfer case. I had them replace the axle and then had the transfer case rebuilt. Then the mechanic that rebuilt the transfer case said it also needed motor mounts so I had the guy the put in the transfer case but in new motor mounts. The U joints were also replaced. Yet I still have vibration and the humming noise. Tires have been balanced, rotated and rebalanced and checked again. Any ideas on what could be causing this vibration. I am certain once I get the vibration gone the humming will go away. Current mileage is 128,000. Thanks for any suggestions.

Previous posts show this turned out to be front wheel hub bearings, scroll down and check'em out.

you have bad wheel bearing, which side is the noise/vibration comming from? once you figure that out you will know which one is bad, typically the front left side has been the problem, but it could be the other side, one piece of advise stop taking you car to mechanics who dont know their heads from their asses, The wheel bearing issue is a very comon problem with all 2nd generation blazer, bravada and jimmys, a new one shoudl set you back about $300 to $400 US and you can easily replace it yourself within an hour, the reason why it is so expensive is because the bearing comes as one assembly it includes the hub, bearing and speed sensor for the abs. good luck

How can I tell what side its comming from? I had my father walk beside it down the drive way and he could not hear anything, I jacked it up and turned the wheels thinking I might be able to tell but I can't tell anything is wrong with the bearings. Going down the road at 40 mph and faster is the only time I can tell its doing it but from that you can't tell where or what side its coming from. I hate taking it to a mechanic until I feel more certain I know whats actually wrong. I think alot of these guys are just guessing at this point. Thanks for the repsonses.

here read over these post, on the link there pretty good explanations :
http://www.automotiveforums.com/vbulletin/showthread.php?t=346082