[gwbas1c]

I can hear when my Dell laptop uses the flash drive heavily. It sounds kind of like a hard drive, so I actually had to verify that I have a flash chip. Apparently it's a known issue; I've assumed that something in it vibrates due to EMF.

[cogman10]

Noise is caused by changes in current. Any pulse of current will ultimately create EMF.

If power lines run anywhere near the sound lines, you are just asking to pick up interference whenever the computer does basically anything. It doesn't take too much of a pulse to be picked up. For a 3.5 jack, the voltage is anywhere from 0.002 to 0.5V. Even a pretty small induced voltage will be audible.