Went riding this last week and my motor sounded like a bearing was going south. If you have ever heard a bad water pump, thats about what it sounded like. Low rpm's (around 1000-3000) and if I got on the gas it went away. I know its not the chain I'm hearing and I change my oil every three Hours. I also use a ratio rite when filling the motor oil. Still using Honda oil. 660 cc, no filter change. 690cc w/ filter. The bike only has about 15 hours on it and I did a thorough break in just so I wouldn't have to worry about something like this! Maybe back to 2strokes? :|