Couldn't find it via google or wowhead. So I'm turning to you, folks.
When inserting Archmage Vargoth into a mission, he has a voice line that is quite annoying. "Looks can be deceiving!" But it's in this high pitched, squirrel-y voice. If I can find the file and then replace it with a blank text file in my sound folder, I'd be much happier.
(Yes, I realize I could just deactivate him, but his combat ally buff is quite good)