i'm glad you like the meta puzzles! it's such a fun concept in general and they were really cool to come up with and develop :>
you don't need to have sound on for this game, dw. there's a walkthrough available if you get stuck, but if you want just a hint:
(SPOILERS)
you'll need to use an item on the black rectangle on the left of the xylophone, and then check if any previous part of the game has given you a hint as to what to use the xylophone for.