ive got a bmw 318i j reg.wen u rev it quite hard theres a clicking noise (like a credit card on a bike wheel)i think its coming from behind the dash but not sure any one know what it is n how to cure it

well the solenoids on the injectors are operating very fast at that stage and normall cause a loud enought noise but this may not be the cause maybe the is engine knock?? check the knock sensors to make sure they operating correctly if its an m42

is it tappets in the cylinder head?, a way to check is to open the bonnet and using a large screwdriver, cup the handle in your hand and hold it next to your ear while placing the tip on the top of the engine while its running.

It works like a doctors stethoscope and you will be able to hear the valve train at work, if there is a tappet on the way out you will be able to clearly hear it using this technique.

it could be a lot of things,
Possibly an injector tick when they squirt, is the sound more metalic or sound ''electrical'' for lack of a better term? if so run some basic napa injector cleaner through it & it runs fine.

try changing ur oil & putting some resoline(think thats how u spell it) in there. l heard this can help

also check ur belt tensioner & also ur idler pulleys (the bearings in the idler pulleys tend to wear out & become loose, which would also create a rattling sound.)