NPCs with custom sounds?

I’ve been on a few forums in my time, and I know that there are few things as annoying for advanced users as clueless dolts like me strolling in and asking seemingly simple questions, but an hour or so on Google and the GMod wiki has got me nothing in terms of answers.

I’ve examined some custom NPCs off, and I now know how to create a simple citizen/combine reskin that runs around and shoots - but I want do go a step further: I want to create an NPC that has its own sounds (I have the sound files already). How should I go about doing that? Is there a line I should put in NPC/lua/autorun/npc.lua?