Actually, no it didn't. I was sure that was it, because the dirt had clumped at odd spots, making the wheel relativly unbalanced. After a quick drive, we noticed no change at all.

So eric and I retured to his house, jacked it up, slapped the spare tire on there and went off again. The noise remained.

It seems its not coming from the tire.

So we took the car back, jacked it up, and spun the wheel as fast as we could in place... and we noticed a potential problem. Every time the wheel goes around, at one specific place, it scrapes something - making noise and slowing it down a bit. I beleive that the rotor is sliding against the brake pad.

Could this be the problem? That scraping I described is very subtle, but I could see this causing the hum/noise.

Also, what's causing it? It happens with the spare and the real wheel, so I think the rotor must be bent or somthing. Wierd. Any suggestions?