Pea whistle steganography

It only takes a little bit of steganography before everything looks like a secret communication channel!

Cool experiment. The biggest surprise to me is that the fluctuations of the real whistle appear to be a fairly constant frequency; I would've expected more chaotic behavior.

EDIT: While we're near the topic, does anyone have any recommendations for acoustics texts/resources? In particular, I'd love something from the approach of analyzing real-world sounds & instruments.