High-pitched buzzers (e.g., the old-fashioned type of smoke detector).
Whispering OR speaking too loudly, especially when the latter verges on shrillness/shrieking. Find a middle ground, will you? Along the same lines, when people do that, I start talking more loudly to compensate, and then the person says "why are you yelling?" Um, to make myself heard over you?
Certain tones/types of voices...some people just sound "whiny" all the time, even when they're just talking "normally."
Ever see that Progressive ad with the guy announcing "Let's get ready to BUNDLE!" and that word is dragged out for at least a full minute? I realize that "he's annoying" is part of the point, but I mute that ad every single time (and, while many people dislike Flo, I don't really have a problem with most of the other ads in that series).
Babies/young kids screaming and shrieking...learned to tune that out, or else I couldn't work where I do. I just tell myself "at least I don't have to deal with them after they leave...that's Mommy and Daddy's job."
Someone swishing their mouth right next to me. Ever have someone do that with their milk right after eating? I've had to suppress the urge to...well, you can probably imagine. Eww.
And then, there are the times when any sound is unbearable...and I can't really fault anyone/anything for that...it's just me. Right now, for example, my head feels like it's vibrating from any noise/sound at all--headache-inducing, and anxiety-inducing. 
_________________
The existence of the leader who is wise
is barely known to those he leads.
He acts without unnecessary speech,
so that the people say,
'It happened of its own accord.' -Tao Te Ching, Verse 17