meineke will charge you @$70-80 to weld the cat and header into alignment, just got mine done in the same area, and it may not be just a leak, most likely a larger separation between the header and cat when the motor shifts under exceleration (sp?). reason it gets some what quieter because of when the motor shifts back and closes the gap, or i could be wrong. also what kind of n1 muffler? apex n1 are really loud without a pre-muffler.