Just tried fixing up a 2007 Land Rover Kaikas MTB, that cost £400 (about $530) when it was new. The front wheel makes an intermittent buzzing sound, that usually lasts around 2 - 5 seconds, and might not be heard for up to a few minutes - or sometimes soon after. This occurs at any time on flat terrain, so it's not got anything to do with going over bumps. Though I did notice when coming downhill fast on the road, I could feel vibration through the wheel. Because it's so irregular, I'm inclined to not think it's the bearing adjustment (I've tried a loose-ish and tight quick release to quickly see if changes in the bearings made much difference, I don't think it did). The wheel spins nice and freely without play in the bearings. Any ideas?