If it gets louder/worse when you turn left, then it's probably the right wheel bearing. (More weight shifts to the right side) If you plan on doing it yourself, I got the bearing for around $45 at Napa and had it pressed for $40 at the same store. (Call around, as only a few Napas have machine shop service) Advance also sells the bearing.
My last noise like this turned out to be the left axle shaft, but I replaced the right bearing first, because it got louder when turning left.
These noises can be a beeatch to nail down. I now have new L & R wheel bearings, new left axle shaft, and new ball joints. (what the heck...)
