I have been noticing a sound/vibration coming from my 05 Z750. It sounds/feels like something grinding or spinning roughly as if a bearing is failing. The sound/vibe is most pronounced when there is little load on the engine like when I am on a flat stretch of road. The vibration is not so noticalbe when the bike is cold but becomes more noticable as the bike warms up. I took the bike to BK but they couldn't hear it and suggested I get the valves looked at at the next scheduled maintenance (the 18K one) which is coming up. Is there anyone who has had this happen to before? What might be the cause? Any help appreciated. Thanks.