DeviantArtist KazeXenami has built/is building a dubstep gun that should someday look like the one from Saints Row IV, and it appears that it could be kinda/sorta/theoretically partially functional, even.
This dubstep gun does have speakers that are intended to work, but it's difficult for my elderly eyes to figure out if it might cause explosive wubs. I'd encourage you younger folks to examine the gallery for clues.
Anywho, here's a couple other shots of the work in progress. And you can click through to the gallery for some more.