'98 Nissan Pathfinder - Weird Noise from Left front wheel.

[cartoon_pat]

I have a very weird noise coming from the left front wheel. It only happens when the wheel is spinning. When it first happened it was constant. Then I came home right away and left for an hour then tried it again and then became intermittent. It's not the usual click click from a CV axle, or the whomping sound from a bearing. It's almost like a rock or something stuck somewhere but I can't see anything. Any ideas?