I've used various things on various cars/trucks:
As far as sound deadning goes, I find that almost anything sold by the aftermarket car industry doesn't work as advertised or is grossly overpriced relative to performance.
That said, I decided to turn to other industries, like ship builders. There's gotta be a good way to quiet down huge diesel engines on yachts, isn't there? I go to a local shipyard outfitter
www.ballard insulation.com. They have stuff called Barrier 155 which is a 1/8th inch acoustical barrier with a quarter inch of decoupling foam on one side. It's pretty heavy and it's fairly expensive at about $5/sq ft. But for under carpet areas it works as well as about 3 to 4 layers of dynamat.
There's another material they don't list there, it's similar to dynamat in that is a peel and stick material. Unlike dynamat you can apply it at room temperature and it does it's job across a wide temperature range. It's a much softer stickier material (like silly putty) with aluminum foil on one side. I find it works really well as an acoustical damper. It's about $2/sq ft and comes in a 1x2 foot sheet. You need about 2 layers of that to get noticeable results when applying to heavier guage steel. I buy that stuff from
www.hamiltonjet.com
Just my $.02
