i just used carpet to deaden the top of my trunk and i have had no rattles at all

 

I piad 100 bucks for the dynomat trunk kit, and while I get more bass throughout my car, the rattle is still there. I don't think it's worth it.

 

go to walmart and get some poly fill. its 7 bucks a box, for the whole car you'll probably need a total of 3 boxes. im going to go get some tomorrow to try it out, but ive heard from plenty of people it works wonders, and at a fraction of the rediculous cost of dynamat.

 

Well first of all dynamat is meant to reduce the amount of acoustic energy that is lost from an absorbant material(i.e. anything that moves at a certain frequency[resonance]) A rattle is obvously two parts that are absorbing different frequencies and are running into each other(if they were absorbing the same frequency they would move together granting they are the same mass). Polyfil on the other hand is a material that can help absorb sound in a positive way but not like dynamat. All dynamat does esentially is add "weight" to a panel to lower its resonant frequency(frequency at which molecules naturally vibrate) so that it doesn't absorb the frequencies in which you want to hear, which is why it makes things sound better and/or louder!!