Don't know what you've checked so far, but I would go in this order:
Check the tire/wheel it seems to be coming from for thrown balance weights, pothole damage, tire tread separation/bubbles, and loose wheel lug nuts. Also, check to see if the vibration changes with applying/releasing brakes.
Then have the suspected wheel balanced. While off, inspect the brakes for anything obviously wrong.
Then, I would investigate the wheel bearings (ask me how I know this one), as they are notoriously earl failure items on many X-s.
Then
