very weird occurrence while listening to black dog by led zeppelin?

[SAЯAH!]

its very strange- i was listening to "black dog" by led zeppelin, and i noticed that my headphones weren't plugged in all the way. right before i was about to plug them in fully, the singing started, and it sounded very creepy- kind of like a chorus of shallow singing at different tones and at different times- i listened to the whole song, and it continued to sound this way. i distinctly remember that the volume of the singing was a bit lower than usual, and the music was a bit off. once i realized this, i tried about every other song i had on my ipod, but every time i listened to another song with my headphones not fully in [just like they were with black dog]. i could not hear the voice and the music was slightly off. i even tried listening to stairway to heaven like this, but i got nothing weird like i did with black dog. now im just wondering what the heck happened! im not suggesting anything paranormal.. besides, i couldn't care less if it was a satanic prayer. led zeppelin kicks ass. just, help me find some explanation?