friend installed a turbo on his 96 cobra. stock basically but he did the coil on plug conversion on it. car is tuned and runs good. but....it pops and crackles, mainly at idle or at decel. it doesn't change fuel trim, i.e., the ratio stays the same when it happens and it does not miss at all. motor is smooth. car has no mufflers and is straight piped all the way out of the back. we are wondering if the cop conversion could be creating this. the early computer is not set up for cop's and not sure if that could create this noise. ideas?