Wheelbearing. I had the same thing happen to mine. You can try taking off the spindle and packing it with grease. I did that to mine and it helped, but the growl didn't go away until I replaced it. The front bearings are all one peice with the spindle, so you have to replace the whole thing, which sucks. A new spindle will run you about $75. As I recall, you have to take the wheel off, the brakes and disk. Then get a big freakin' breaker bar and take off the nut in the center of the hub which is behind the domed, rubber covered cap that is in the center of the hub. You can pry that off with a screw driver if you're real carful. Try not to rip the crap out of the edges though. Just tap it under with a hammer and pry gently. With that nut off, the spindle comes off and you can replace it.
Oh, and when you take the calipers off, use some wire or something to support them out of the way. Don't let them hang from the brake lines. It's bad for them.
If I forgot anything, anybody feel free to fill in the blanks.