Dry Ice... You put dry ice over the sound deadener... Let it sit for 5 minutes... Remove the dry ice and take a hammer and smack it... It shatters and comes right up...
What kind of sound deadener? Like Dynamat? If so, then yes, heat it up real well in 1 foot sections and it should lift right up with a little persuasion. Then clean up the residue with acetone.
You can use the left over dry ice; smash it up, put about two cups in a pop bottle with a lil less than a cup of water, cap it and throw it in your neighbors backyard.:gr_stretc