If there's room for an amateur opinion--I'm not so sure about the bearing idea. It never hurts to check, but when I've been around a bad wheel bearing, it always had a lower pitch and made more of a rubbing or grinding sound. If it were I, I would first check to make sure that the lug nuts are tight. 2) I'd check to make sure that the brakes aren't rubbing. 3) I'd do a thorough inspection underneath. Try to see if something looks worn or if part of the suspension is rusted out. It doesn't hurt to tug on a few things underneath to make sure that they don't have too much play. (Just make sure that the wheels are blocked before you tug, of course!)
Anyway, let us know what you find!
