I just got a Mac o/r H pipe installed on my '01 Cobra. There is an annoying ticking/hissing/vibration deal coming from what seems to be under the drivers side dash when i accelrate (very noticible low rpms). Can't tell if it's inside the car or not. The more gas i give it, the faster and worse it gets. Is this normal vibration or could I possibly have a leak, although the guy who put it on said he checked for leaks and there weren't any. What is going on... Thanks.