It's definitely leaking, i separated all the joints, sealed them, no resonating in the cabin at all, couple of days later and it's doing it again, it's beginning to bug me now lol!! Know what you mean about the defuser and I remember you saying about it before, sure the heat shield doesn't help....i don't think it's ended the same with an aftermarket exhaust, it's a distance away from any heat, possibly heat reflective tape would be sufficient?