need ideas

[WESTCOASTER]

wondering if anyone has any ideas ..i own a 3l rb30 carby model nissan patrol which has a noise coming from me extractors which sounded like the gasket had gone . after changing the gasket it is still sounding the same inwhich i thought maybe a hole in the extractors them selves, there are no sihns of any holes or leaks from around the pipes at all that i can see, i even used a mirror to look behind the pipes ..it was doing a bit of back fireing a while ago (minor).could it be an engine problem and noise coming through the exhaust?

[Woof]

Hey mate, it is always a good idea to post up an introduction before asking any questions..........just gets everyone on side from the start.