I give up.
Wait... here's a long shot.
Maybe one of your cones is coming loose as you ride, and tightening up the hub bearings... and heating up in the process.
Or you didn't account for the quick release pressure, which tightens the hub bearings in the closed position. Try adjusting the wheel hub so it has a little more play, just a little click in the axle when it's out of the bike.
A little loose won't hurt anything.
When you stop to clean things, it cools or something and is ok for a while.
Is the grinding only while pedaling, or all the time?
Last edited by duckforcover; 09-12-10 at 05:18 PM.