I have a 99 Cobra and I am having trouble with my exhaust. I have Jba headers which are conected to a 2 1/2 inch bassani off-road x-pipe. I also have spintech mufflers. However, the car sounds horrible. There is poping noises when I get off the throttle, I know this is due to the lack of back pressure, but why does the car sound so raspy and out of tune?? Also, If I have an X-pipe with cats would the problem be any better.