For the removal of sound deadening to save weight or whatever your reason be, there are 2 good methods you can use...
1. Hammer and chisel.
Get some tunes and a mate and maybe a beer and start hammering and chiseling... You WILL need to repaint the metal afterwards as you would have no doubt scratched some of the paint on the metal underneath the sound deadening from the chisel.
2. Dry ice.
Grab some dry ice, dump it on the deadening and throw a towel over it.. leave for about 2 mins and then move onto a new section, hit the "iced" section wit a hammer and it will shatter, adn sound deadening will shatter away.
This mod is mainly for race cars that are trying to save all the weight they can, the removal of carpet/sound deadening etc DOES make your car quite a bit noisier, but you'd be surprised how much the final amount of sound deadening you throw away weighs.... I know I was.