This is a case of DIY gone bad, if I had to guess. IMHO, most folks who wants to put car shaking power into their car need the help of a professional.
All these problems are faced by professional stereo installers every day, and there is a range of techniques and products that have been created specifically to deal with it.
Dynamat is your friend. Learning how to apply it is an interesting experience, however. Best installer I've ever met used a signal generator wired directly to the car amplifiers to produce specific frequency tones, then he would crawl around inside, under and around the car, marking spots that needed dynamat. Using this technique, he produced several cars with literally deafening sound that did not rattle even the slightest bit.
A bit of a safety note, however.
Personally, I like a balanced sound, something that isn't heavily overbalanced to the subs. If you have mids and highs to match a system that rattles your mirrors, you'll also have hearing loss within a few years. It's one of the things that catches up with you when you start to get a bit older, and if you make it there, you'll regret it.
Furthermore, if you can't hear the sirens from emergency vehicles over your music, you have a problem. I knew a kid who got hit and killed by a train from behind because he was listening to his iPod too loud while walking town the tracks. Another friend of mine lost his son when he didn't hear the horn on the dumptruck that lost it's brakes. I've personally witnessed a Mercedes get creamed by a train at a crossing because he had his music turned up loud enough that he couldn't hear the train's horn - and those things are LOUD.
Don't get me wrong - I'm not against good car stereos - I have one myself, and yes, it's more than capable of drowning out conversations in the cars around me. However, I'm careful when I use it, and I keep in mind that it reduces my awareness.
