I still find it very strange that it would work. A CPU can have millions of transistors changing state at any given moment, in an asynchronous out-of-order fashion. Add to that all the other components in a PC, bus talk, etc. Even if we got an accurate print of all of the digital chatter happening in a PC, it would be nearly impossible to derive anything specific from that. A power filtering coil is an even much more crude component. You can hear big changes like CPU/GPU frequency stepping, but that's all.