What's happening in disk 13?

Truth about disk 13. (Not Finished)
If you've been playing Minecraft for a long time, you already know what disc 13 is. Its a disk that plays an eerie recording of bells that are being rung in an unsettling way. But have you ever wondered what is happening in the recording. Where the sound is coming from. Well that's what I'm here for. To tell you the truth about disc 13.