In Episode 110: Mapping of This American Life there’s an act that leads with a discussion of the background noise we hear all the time from appliances at home and in the office – noise that, like all sound, has a particular pitch.

“For some reason I had been thinking about why it is that we seem, almost universally, to assume that a minor chord is sad and a major chord is happy. If a minor third is just somehow inherently sad, then if I were sitting in an office having a minor third played at me all day long, then it’s indeed possible that I could be made sad by just sitting in my office.”