Your friends will abandon you.
The first time I heard that ringing in my ears, it freaked me out. Wandering into Ahn'Qiraj-40 and having C'Thun whispering sweet evil nothings in my ear about my heart exploding and being already dead is hardly someone wants to hear on the best of days, much less while raiding. Warcraft has had a history of strange and dreadful whispers, sometimes from places in the game and sometimes from actual items (Chained Essence of Eranikus, anyone?). And they always seem to be strange and terrifying. But what if they weren't? What if they were comforting or gave you courage?
The idea that a familiar, friendly or helpful character from WoW guiding you either by being in your head or being a part of an item you carry seems a little alien, but to me, like a warm blanket for your character. Maybe it's a certain dragon aspect watching over you, or the familiar voice of your Orc mentor telling you try again. It would inspire confidence rather than fear, congeniality rather than hostility.
Would you go along with the voice or not? Who would it be? Or do you find the idea of anyone whispering in your head (quest mechanics aside) a little weird or violating?