pixel_player933292123
Best to watch the YouTube on this one. I think this puzzle is a bit deceptive. What you initially see is only half of the song. First you have to enter the notes of music that you see in the two rooms below, and then later you have to change the notes to match two more bars (not shown until you access a secret level). And it's confusing because after you find the secret level, the second half of the notes are shown in the same rooms with the first half. You have to deduce that you need to switch to the red notes after you have already completed the first two bars of the gray notes.
https://www.youtube.com/watch?v=T0ex6um14EE&feature=youtu.be
The third test starts at about 13:55.
Diggy finds an important sign in the blue room on the left that says something like..."If you can't remember the notes to the song [Mary had a little lamb] you can find the secret under the Bulls horns."
Heads down to the next level.
Goes to the NW corner and breaks the hidden tile for the Bulls horn column.
Goes down those stairs.
You can probably take it from there. Note: There is one more hidden tile along the way.
