Over 20 years ago as a young teenager, my friends and I would sneak out in the middle of the night and toilet paper other people's homes. One night we decided to walk or cut through a cemetery. More than halfway through, we heard something and we all stopped. It wasn't very loud.
There were four or five us. It was the "Happy Birthday" song... I don't remember the instrument or if I identified the instrument playing the song, but it was like the song was being played on a record player because part way through the song slowed down and stopped before the song was finished.
We argued a little bit about where the sound came from because we could not tell from which direction it was coming from, but it was definitely from somewhere in the cemetery. We got out of there pretty quick.
As far as we could tell there was no one there but us. It was a very strange thing to happen in the middle of the night in the middle of a cemetery. We had walked through that cemetery before in the middle of the night without anything unusual happening.
After that experience we went back again on another night to explore or figure out where the sound came from, and we didn't notice anything unusual. Also there was nothing else near this cemetery to make the music. It was surrounded by empty cotton fields for hundreds of yards in every direction.
I'm not sure we all agreed it was the Happy Birthday song, but we all heard it.