My first system I had was a JL Audio 8.3 Microsub (3 8W6's, 140.1 DB on a Audio Control meter about 10 years ago now) in the hatch of a Firebird with a PPI PC2150 Amp. I knew a guy that went to one of those wholesale flea market type electronics sales and he came back with some Legacy equipment. I turned my system on and told him to sit in the car and he refused. He said its not what it sound like on the inside, its what it sounds like from the outside. So he procedded to ask me what I had so I showed him. In the trunk was the amp, sub enclosure, and a .5 farad capacitor. He pointed to the cap and said thats where I had spent a lot of money and that is why it sounded like it did. I said no and he got defensive. I told him to come back when he got everything installed and we could compare.....but never saw him again....
Point of the story, make it sound good on the inside, and if it rattles on the outside get some sound dampening material.