...When I add a custom sound for a model. For example, Cheeto's PPSh. I replace "tommy_draw_slideback" with "ppsh_draw_slideback" and put in a custom sound edited from CoD.

When I spawn/pickup a PPsH as a Brit now and it plays the sound, the game freezes and crashes. What gives?

If the sound is improperly formatted. I has to have a start marker, has to be 16bit, 22khz, and make sure there's no looping marker.