When I ride my bandit for more than 10 minutes, I get all numb in my rear end due to vibration from the engine. Is this normal? It's no problem at all up to 6000 rpm, but above that it gets more distinct. I'm sure it comes from the engine, because if I engage the clutch, it goes away. I'm not sure if it's supposed to be like this, it's not that big of a problem. I was just wondering if there is some rubber bushings or something that could be worn out? Can there be eccentricity in the flywheel or anything like that?