First off, I'm being completely serious. This isn't a creepypasta or anything, so please hear me out.
Ever since like a week ago, I've been hearing a really ominous, sort of faint growling sound in the background while playing. I've heard it on 3 characters, all different classes. I hear it about once every 2 days, so it's not something that's constant. I can't remember all the exact places I've heard it, but I'm pretty sure I've heard it on Eastern Kingdoms, Northrend, and Pandaria. The last time I heard it was in Valley of the Four Winds on my Priest, which was what lead me to post this thread. It sounds like a man, with a very deep voice. If I had to compare it to something in-game, I would say it sounds like the Sha's voice actor. However, I'm not certain of that. I also haven't downloaded any new addons since the first time I heard it.
Has anyone else experienced this? I really can't think of any explanation.