I had heard once that you could use the rubber ice dam stuff (to put under
the shingles on a roof near the over hang) from the hardware store as a
cheap alternative to dynamat - anyone else heard that.

http://www.certainteed.com/CertainTeed/Undefined/Roofing/Prodindex/Shingles/
Underlayments/RoofingUnderlaymentsSplash.htm

http://www.dynamat.com/auto_floor.htm

I was thinking of pulling out my back seat and putting a payer of that there
and over the back deck.

Your thoughts?
Tom