i jacked the truck up today and checked the bearings, no movement that i could see but i'm thinking this must be what's wrong. my front left wheel lugs loosened up a few months ago during winter, only reason i found out was when i drove to idaho and had the window down, heard a plastic scraping sound and found the wheel was loose. tightened everything up but i think driving over 500 miles with a loose wheel probably destroyed the bearing.

 

So what was the answer to the problem? Did you fix it? I have the same problem!!!