What do you think the most annoying sound is?

Name the game, then describe the sound (or link a file)

Mine has to be:
Robocraft, the "Your Plutonium Reactor is under attack" sound

Not that the voice is annoying, just the frequency of it. I've literally been driving out of my base after defending for a bit, and then here that sound.

So yeah, what's your least favorite sound?