Read all the info on this site:
His prices are not the cheapest but the information is great. You will understand soundproofing after reading.
Most think dynamat is soundproofing and it is not. It is sound deadening, just stops the vibrations of the metal. It does not absorb sound.
That is why I used Mass Loaded Vinyl (MLV) throughout the car. In fact, I used dynamat then MLV. On the floor I used MLV with a foam backing.
After reinstalling the dash there is a significant reduction in noise from the front of the car.
When I open the sunroof with the cover still closed I cannot even hear the sunroof raise.
It is very nice to have a quite clean '04.
I still have to do the door panels. They will be next right after I install the 8" LCD monitor in the dash.
I bought the MLV from TM sound proofing, they had the best price.