[pbs911]

Fans: people have said they noticed a difference when they changed fans. Since there is also a distint noice from the air cooled motor, it must be the fan. But then again, other cars have fans and don't make that sound.

Chain: Interesting. Although other cars have chain driven components, the Porsche motor does emit a unique sound. It's as identifiable as a blown motor (that is a motor with a blower.) And the Porsche does have all those chain ramps and tensioners to increase the noise level. So it could be the chain.

At this point I'll pretty much believe what you say. You could convince me of either one. That said, I voted for the fan b/c that's what I always thought.