starter problems...please help!

so, i've had my bmw for just over a year now and ever since i bought it the starter has been really scratchy. it still starts but some days are better than others. if i start my car up in the morning, it takes a normal amount of time to turn over however if i turn it right off and start it back up it turns over super fast and scratches as if i was holding the key for too long. anyone else have this problem or know what i can do to fix it?

NEVER! EVER:banghead::banghead::banghead: continue to hold the key AFTER the car has started... it messes up the starter for some reason, had a few people do that and it messed up their starter after a while...