Originally Posted by *****ed4v
id say wheel bearing
i had my front-right bearing replaced under warranty at 12k miles. It began like a hum that I really thought was tire noise, but over the course of time it got louder and louder (even after rotating tires). Finally, any time I was over 40mph it was ROARING.
Dunno what the OP's hum sounds like, but if it gets any louder with time or is still exactly the same after moving tires around, I vote for a bad bearing.