Another observation is that they're either idle sounds (pen clicking, finger tapping) or necessary secondary sounds made during some activity. It's literally impossible to unwrap a piece of candy without making some noise, and damn near impossible to stir a liquid without the stirrer hitting the container once.

>id guess if the sufferer expects we all dislike certain sounds, causing them intentionally is especially hateful?

I think it's pointless to attempt to look at it rationally, given the reactions I've heard seem entirely irrational and disproportionate.

I remember one time I was at work and a coworker on the opposite end of the room was using what I thought was the exact same model of mechanical keyboard I was using, with blue switches. I had never realized just how loud those things were until then. I kept glancing at him and could feel myself getting unreasonably annoyed, but I really had no grounds to say anything under any circumstance, given I had been using those very same switches in that same office very recently. What really struck me was how the same noise would sound pleasing when I made it and annoying when someone else made it, and I wondered if I had bothered someone with my typing, or if it was just me. I don't know if I'll use my own keyboard with clicky switches if I share an office with someone again.

Silent keyboards (and mice!) are a blessing; and not just in an office environment.

That's like hearing one side of a phone conversation, where the utterances are nonsensical because you are missing half the context

When you are typing, the clicking is concordant with your finer movements and the text you are writing. When someone else is typing, it's not.