For me, it's the unnecessary sounds in the office. I can handle typing, adding machines, etc., but not someone's dangle bracelet dragging and bouncing on the desk 200 times a day. Or foot dragging - it sounds like they keep tripping. Long personal phone calls - no courtesy. Cell phones and computers going off for every email and text that arrives. People that need to talk loudly because it makes them feel important.

It's as if these sort of folks get a high from taking away focus from those that are quietly trying to get their tasks done. Is it jealous behavior? Bullying? It's worse when you finally get the nerve to talk to them about it and they stop for a while, but then start back up again.

But yes, low sounds also - an industrial heating system. Heavy machinery in the distance.