Check all of your bolts throughout the exhaust system, from where the header bolts to the cat, all the way to where the axle back bolts to the bpipe. Try to feel for air leaks while your car is running...jack it up, start it, and get underneath.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
Team B.O.B.® - Ballaz on a Budget