The most irritating user noise I have ever encountered in a library was when I was working on music manuscripts when there was a woman across the room whose laptop went BLEEP at every keystroke. And she was typing fast enough that I was getting BLEEP BLEEP BLEEP as an out-of-time percussion part to every tune I was trying to hear in my head. Being a Windows user, she didn't have a clue how to turn it off.

I tried to get her thrown out on the spot but the best I could do was embarrass her into never coming back (at least I never heard anyone do that again).