Bike has about 2500 miles on it. I got it at 1900 and it's been fine. Yesterday I noticed that once I hit about 20 MPH I hear a squealing sound. If I rev at a stop, no sound. The best description I can give is an automotive belt squeal. But it's not noticeable until 20 MPH then it's obvious. Pulling the clutch in at speed seems to make it stop. Any ideas? Thanks.