[nitrogen]

Could those high pitched sounds you recorded just be capacitor whine or noise on the power supply? All cheap sound interfaces in computers produce noise that correlates with CPU, GPU, or bus activity, and many power supplies make squealing sounds that can be heard in quiet rooms. It's conceivable these could be manipulated as side channels in an already compromised system, but they exist regardless of compromise.

[zdkl]

That's the beauty of such methods. Anytime an avenue for compromise seems "noisy", I'd be willing to bet someone smart organised and well funded has investigated using it for hi-value penetration.