It seems like there isn't many things the HD rumble feature can do. But Youtuber Indanam was playing with the new game Game Builder Garage on the Nintendo Switch, and found that they allow you to program the frequency of the rumble. Since music at it's core is just frequencies, you can make melodies with your Nintendo Switch controller! It took some math to fit the song into it's basic block coding limits, but Indanam ended up pushing the limit of the Joycon, and maybe even creating a new genre of music in the process.
Video credit: Indanam