My 1999 Explorer Sport has a nasty hum under the front end. It sounds like I have 35 in. mudders under a 6 in. lift. I started with an alignment, wheel balance a rotation- no help. Replaced the front shocks- no help. Replaced the front ball joints- no help. The only time it does not hum is when the steering wheel is turned to the right.

I am pretty sure it is not the tranni- as I can drop it into nuetral at any spend and the hum is still there. I also topped off the gear oil in the front differential. It started about the same time my ABS light came on (the brakes seem to work fine w/o the ABS activated). Could it be the ABS system causing the brakes to rub slightly that I am hearing? Or something else?

 

Had same problem, I replaced the front bearings and seals, and it stopped.

 

I agree with tthe above comment, your problem is the front hub bearing. It will be expensive, but they are pretty easy to do yourself.