system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the chirping noise that computers make.

I always just assumed that its coming from hdd, optical drive or fan. But recently I got a new ultrabook that has none of them and I can still hear that chirping, sounds like diskette drive but higher pitched. However I cannot hear that sound on a phone or tablet, only on computers.
gpt
It's most likely "Coil whine"

There are small coils in your computer that are used to "smooth out" the current (and capacitors that do the same for the voltage) - electricity isn't perfectly regular, it has little bumps and waves that can damage your components inside the computer: the coils help make it "smoother" so that your computer lives longer and works better/more efficiently.

When the current passes through these coils, though, they vibrate quickly and rub together, creating a high-pitched chirp.