from my little bit of experience here's what I know... It is common to see a small amount of fine "metal shaving". If you're talking the size of a finger nail trimming then you're probably grinding some gears or your prop shaft is slightly bent. When you shift your motor into gear you should not "baby" it. You should bump it into gear quickly. If you're babying the throttle into gear you can hear the clutch dog bumping the gears. Not 100% sure if this is what is causing the metal shavings but it could be i guess. If the shavings aren't that big and everything seems to operate fine then I wouldn't worry too much. Just my opinion. Hopefully someone else with more experience will chime in.