I don't think this issue has been reported for Minecraft Java yet, but I was just chilling in my 1.16 singleplayer world when I heard this weird soundtrack, which is for the nether, playing in the overworld. A link to a video of me going to the nether and coming back to see if it was still there in the nether or if it continued playing when I went back to the overworld: https://www.mediafire.com/file/tc0zuji5oy8rrr5/Minecraft_1.16_-_Singleplayer%3B_Nether_Playing_in_Overworld_Report.mp4/file