Acoustic Cryptanalysis ... "coil wine" generated by capacitors ...

Many computers emit a high-pitched noise during operation, due to vibration in some of their electronic components.

Unbelievable, look at:

This makes perfect sense. On many computers it is easy to hear the fluctuations, although it never occurred to me these can be analyzed.

The old tv,s made noise too . And it changed with the video. And wire carrying hi power makes noise too. Lighting dimmers too. There is compliance codes for the allowable noise emissions these can make . Both sound and electronic on the system wiring . In data centers we oversize the neutral wire for this purpose too.