Just experienced a problem with my 00' ex 500. I noticed a whining noise coming from the rear end of the bike. It kinda sounds like the tire or brakes are rubbing, but i can't see any evidence of either case. Funny thing is, when i stand up on the pegs, the rubbing noise goes away. Bad thing is, the noise is getting worse, so I have to stop riding. Any suggestions on what my problem my be?