So its hard to hear (you really have to turn up the volume), but Kayla found the sweet spot on the book (it makes a noise) in her command center, and kept opening and closing the book over and over today. Briiiiiing, Briiiiing, Briiiiiing... After 3-4 of the book noises she would exclaim "ahh" then proceed to repeat the whole process over again.
I finally turned to her after hearing it for the 400th time and asked "What cha doin'?" She stopped messing with the book, made cute faces, and stuck her hand in her mouth.
She's a quick learner -- she already knows how to work the system.

Edit: She started it back up after I posted this, and she opened/closed the book so much its now broken. The sound occurs now without any provocation over and over. I had to remove the batteries and take a tylenol.