If one Minecraft world is opened then closed and then another world is opened, multiple pieces of music play at the same time. Adjusting the "music volume" does not apply to all the music being played, and some of the music being played even remains on the pause or menu screens.
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However, this issue has been closed as a Duplicate of MC-35856.
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I noticed this too, the only way I could find to temp fix it is to quit the game back to the launcher and restart.