I am looking at buying a 2001 660 from a friend. It has a "clunk" noise from where I believe is the crank case area. It occurs when I engage the starter and when I shut the engine off. It's not 100% consistent, but it occurs very often. I am a auto mechanic with little knowledge of this engine. I originally thought it might be the starter, but it seems to be lower in the crank case. The machine does not seem to make the noise once it is running and seems to run and perform good. Is this a common problem or a sign of a more serious problem that I should keep away from? Of course, the owner doesn't have a clue to what the noise is. Any ideas?