Had a funny noise could feel a knocking with my foot on the clutch side at about the speed as the clutch turns, thought that something had happened to the drive shaft. after inspection I could not find a thing, but still had a funny vibration that went away after a mile or so. After getting home and taking another look I fond these marks on the primary clutch they cover about 1/3 of the inner face, Any Ideas what might cause this? and the belt looks just fine.