Prop up the front end and spin the wheels by hand so you can hear it close up with the engine off. Could be bad bearings? I can't think of what else could cause it unless you've got some debris caught in the wheel.
I had what (by your descripion) the same noise. I aslo thought it was coming from the front tires. After having the quad up on a lift while back i spun the wheels and no noise. I i went and pushed it around the driveway. (my neighbors already think i am nuts so no biggy). As i pushed from the shifter side i noticed it was actually coming from the chain guide. The chaing was just rubbing on it and i think that is pretty normal for the 700. Hope this helps.