Completely off topic sidenote: even when completely muted, my MacBook Pro (Retina, 13-inch, Early 2015) makes a sound when hovering over the names in the first chart, and a different (deeper and quieter) sound when hovering over the second one. The sound appears to come from below the F2/F3/2/3 keys. I tried to record it, but its too quiet and there's too much background noise here to hear it on the video.

Anyone have an idea what this would be? I presume it's the CPU/GPU underneath, but I've never heard this before. Does this happen to anyone else?

With my Fall 2011 MBP, it's the wall wart that produces a wide variety of sounds depending on the CPU load.

Desktop motherboards are known for high-frequency sounds in response to varying load - the source are the low-voltage regulators for the different CPU domains.

That's interesting. Stick an old fashioned AM radio near it and see if you can amplify the sound.