| Mine had similar problems until I loosened the chain. A buzz at around 30-35mph with vibration through the bars and a howl at around 60-65mph (twice the frequency?). I thought a rear wheel bearing, or worse the gearbox output shaft bearing, was at fault. Make sure that there is at least an inch and a half movement of the chain. This is more than the manual says but it seems to need it. I know of another ST4s owner who has also experienced this. |