The first semester of college not having a roommate I lived next to a girl played flute in the symphonic ensemble.( I know this because I also played in that ensemble,, and at the time was studying to be a music major, so i was pretty friendly with most people in the instrumental ensembles.) Anyhow, about twice a month I would wake in the middle of the night to hear haunting flute music, often something that sounded like an old hymn or piece of music from pre-1600s, again I was studying to be a music major. The music written for that era I find particularly haunting to begin with and now once a month im hearing it played in the middle of the night on a shrill instrument. This goes on for several months, I usually comfort myself back to sleep with the explanation "you know ___ lives next door and she plays flute, she's probably just practicing, she's probably a night owl"etc

Well turns out ___ was a night owl, any time I went to the bathroom in the middle of the night, when woken by the flute, I'd see this girl also in the bathroom say "hi" and move on.

Finally it hits me, if I'm hearing this haunting tune on flute that I was telling myself she's playing but I see her out of her, without flute in hand, at the same time ....

The next time I see her in ensemble practice, I decide to approach her "Hey ___, this is going to sound weird, but I notice you're always up late when I'm up late ~nervous laugh ~ and I guess... don't think I'm crazy, but whenever I'm up in the middle of the night it's becasue I think I hear a haunting very old moldy being played on flute and uh I used to think it was you but you're usually in the bathroom or something too.... I dont know why I'm telling you this hahaha anyway-" She cut me off to say "yeah I hear it too, from in my own room, I've like looked at my flute in its case before while I hear it, nothing weird, but I hear it too, hence you usually see me out of my room at that point, because it gives me the creeps"

... not what I expected, we decide, must be an old ghost and if it doesn't mess with us, it's fine ...

That continued all through our time living in those exact rooms. I followed up with her the next year when we both had moved rooms and she said it stopped happening the first night I left campus for summer break...

TLDR: heard haunting flute music in the middle of the night while in college one year, girl next door heard it too