hello i have just got my erst back from being re built and i have run her in and everything even thought its run in still taking it easy but i have a little play now and again. when i put my foot down and the revs get to 5k there is a noise from the exhaust which sounds like a machian gun whats is it anyone have any ideas o yeah it is running airfilter exhaust and a piper cam but still the standard ecu (running in purpose only thought)