dude the rumbling sound is all about it man... thats what makes the whole sound so special... even the astons ve em
neway wat u want is a performance header and then a straight pipe connectin to ur exhaust and ull get a crisp roar .. what i guess is your looking for
just adding mufflers is not gonna do you any good ... tried and tested on my pailo 1.6 so tellin ya and plus your throttle response improves too