I've heard such noises before on my PalmPilot Professional. In a quiet room, I can hear a distinct hissing sound when I turned it on.

Capacitors can also play music apparently. During audio testing of a speaker system in my company, I could distinctly hear music coming from a speaker board with no speakers attached. It turns out I was hearing the audio generated by the capacitors on the board.

My combination of gigabyte f2a78m-ds2 and AMD A8-7600 has a hum that I can listen to how hard the gpu is working as I scroll through a web page. Thankfully our MSI boards do not make a noise.

I've got a sony laptop that I can hear scrolling through the audio; it's kind of a bummer to hear these buzzes and digital groans.

I think the coils are making the noise not the capacitors:

https://en.wikipedia.org/wiki/Coil_noise

Almost everything starts to make noises at higher currents (e.g. CPU voltage regulator). You have of course coils making noise, you have ceramic capacitors making noise to due piezoelectricity, even good old fashioned electrolyte caps can make noises and transistors buzz due to thermal expansion of the die under switching stress. Not in computers, but even batteries, cables and bus bars make noises under pulse current loads, as do film capacitors (used in high power snubbers).

In the case of capacitors it also goes the other way; tapping a capacitor induces voltage spikes which can disturb analogue signals.

( the last part is an actual reason to isolate amplifiers from speaker systems. Not usually worth it aside from the very high-end. Not as much effect as isolating a turntable for sure, but theoretically it should make a difference. )

It's often both. Capacitors also have a capacity (hah!) for making noise. Coils generally get it first since they are a more straightforward electromagnetic device.

Ceramic capacitors still make noise (and can pickup noise) thanks to the piezoelectric effect. Coils typically make more noise though.

I've got an ASUS board P8Z68 Deluxe that sings like you wouldn't believe. Drives me nuts, I just wish I could silence - but I suspect that would require new caps...

Or just pour generously with hot glue on top of suspected caps.