new engine noise

[Aaron K]

So, after finishing up the last autocross of the weekend, I notice a new
noise coming from the engine or the near vicinity. :( My car is a 91 sentra
se-r, and its got abotu 122k miles.

At idle, its a metal on metal noise, and when you rev it up, it diminishes,
but you can still hear it through the rest of the normal engine sounds.

I tried disconnecting each injector in turn to see if it got any quieter,
but that only caused the noise to be more pronounced at idle, which I might
be due to the engine vibrating more (leading me to think its external).

It got a new timing chain tensioner about 12k miles ago. Could this have
already gone down the tubes causing the timing chain to slap up against
something? I've heard of other people say something about an alternator bolt
being loose, making similar sounds, and last time I checked nothing was
loose there (although I was unable to detiremine which bolt was supposedly
loose on others' vehicles).

I know its hard to comment on a noise described via email, but I would
certainly appreciate any feedback.

Thanks,

Aaron K