a couple of days ago i rode my 400 and noticed that it made a noise on the left side of the engine when i started it. it sounds like a really loud grinding noise, but goes away when i ride it and bring up the revs and will only come back it i start it again or have it idle for awhile. i took off the left case and was looking around the flywheel, there are some metal shavings and the gear behind it spins freely to the right but not to the left. any help would be great thanks.