User:Piccobello/Hissing sound on battery
It took me a while to realize this.. the sound seemed to not depend on CPU in any way: it would always start when I unplugged the power. I then realized that the sound would stop when the screen was off, and that I could start it while on AC power by simply decreasing screen brightness.
Only at full screen brightness the sound would stop. There is a BIOS setting that regulates that: simply switching Config>Display>Brightness from Normal to High solved the problem.
This means that my batteries will last less, but if I'm in a noisy environment I can still decrease brightness manually.
I noticed another much weaker sound that seems to be turned on whenever I switch to the performance governor, and is only turned off if I switch to powersave, regardless of wether the battery is used. This does not affect me as I never use the performance governor.