There is a bug where every 20 seconds or so, a Cave Sound plays. This happens anywhere as I've discovered: Underwater, Surface on land, and The Nether. I have not been back to the End yet. This is a Survival World, 150+ MB, cheats were never activated and I have beaten the Dragon. Even though the new Beta update says it was fixed, for me it hasn't. It is like a /playsound command, it doesn't follow you and you can walk around the sound once it plays at your location.