Could be coming from your brakes also. Have someone else in the vehicle stick their head out the window while you drive slowly and see if they can tell which wheel the noise is coming from - that'll at least give you a location to start looking. Then you can jack up that corner and rotate the wheel by hand and try to determine where the noise is coming from. It could be something as simple as a rock caught in the brakes or the brake backing plate making contact with the rotor after having been bent by hitting something in the road.

At the very least it'll give you more info to post for suggestions. <img src="/forums/images/graemlins/wink.gif" alt="" />