weird noise in my engine bay

[chalmer240sx]

i drive a 1990 nissan 240sx and last night i heard this really weird noise under the hood and after i started to let the clutch out. the noise only does it on decelleration im not sure what it is. any ideas? its a fast rattleing noise

[Ignoble]

Might be something loose? Heat shield on catalytic converter rattling due to vibrations? Transmission gears vibrating due to thin gear oil? Throw out bearing gone bad? Not too sure but just throwing out stuff.

[Vegascorbin]

Not much to go on but I have to throw out the idea of timing chain and guides.

Have you done anything to the engine lately?

[chalmer240sx]

we figured out what it was. my fly wheel fell off due to the fact that when we did the 5-speed swap we used the automatic flywheel bolts.

thanks for helping though

IF U DO A FIVE SPEED SWAP DO NOT USE AUTOMATIC FLY WHEEL BOLTS

IT WILL COME OFF AND POSSIBLE STIP OUT THE THREADS IN THE CRANK CASE