Museum Duck Puzzle

[Demon_King]

I found the cases off to the right of the musical ducks are obviously pointing towards other levels. There is also a duck next to it that makes a sound similar to one of the notes. This might be a puzzle that reaches throughout the entire game.
Top left: Unknown
Middle left: Affair with Death
Bottom Left: Call in Dead
Top Right: Possibly Toxic Love
Middle Right: Unknown
Bottom Right: Unknown
This is just a theory but it's definitely worth investigating.