Aright, so I'm getting a 12' JL subwoofer for my 04 volvo s60. Should i worry about the rattling being too bad or will there even be rattling?

 

its been a while since you posted but ive got a 12" sub pumping 250 watts and the rattling from the outside of the car is minimal. from the inside you simply cant hear it
but remember to always crack a window while blasting your subs, otherwise you might do things like blow out your tail lights or sunroof (happend to me in a different car lol but that was 1500 watts)