alright so i have a complete bone stock JDM GSR B18C and i installed a brand new in the box Megan 4-1 Header and im running a full buddy club cat-back exhuast system with stock cat but now my car sounds like a subaru has a rumble sound to it i dunno what it could be i check for leaks and dont seem to find any but i think it's leaking were the dounut gasket goes would that make it rumble like that???? it's annoying driving it cuase litterally sounds like a suby lol