Ive been thinking about sound deadening/proofing materials for a while now, and i think ive come up with a good cheap solution which should work really well.
Being into car audio too, ive got some sound deadening in my car already. Instead of expensive smelly dynamat i found out on a car audio forum that you can just use roofers sealant tape instead. Its exactly the same stuff, but about a 1/5 the price, and it doesnt smell. For about £5 ($8?) you can get a strip 3m x 25cm, plenty for a computer. This is the base and should sort out any case vibrations present.
Then on top of this goes a layer of carpet underlay. The underlay i have in mind is made of a substance which is somewhere halfway between a foam and rubber, and the surface has lots of bumps over it (best analogy i can think of is like a small mogul field from a ski slope

) This gives it a higher surface area with which to absorb high frequency air-borne sound.
I think this combo would be good at absorbing vibrations as well as absorbing high freq. noise. Im gonna try it, so ill let you know how i get on. Hopefully the underlay shouldnt cost much, if i cant blag some free as a sample. so should cost about £5~10 for the whole comp. Not bad compared to about £40 for the proper stuff.
Has anyone else tryed using various materials for sound deadening? If so how have you got on?