Why are screechy noises so unpleasant?

THAT'S THE WHY:Nails scraping down a blackboard. It would make you wince just thinking about it. And what about train wheels grating? Or a scratchy violin?

Why is it that screechy scraping noises are unpleasant to so many people?

Researcher Trevor Cox, from the University of Salford, sought to answer that question by conducting a web-based experiment in which users rated each of 34 awful sounds for their horribleness.

Vomiting, microphone feedback, multiple babies and a scrape/squeak like train wheels topped the charts. The scratchy violin mustered a valiant sixth and, interestingly, nails on the blackboard was decidedly mid-range horrible at 20th.

One theory for our aversion to such noises is that they resemble distress calls of some primates. The experiment suggested that we tend to have an intrinsic dislike of scraping, but found it hard to completely back up the notion that it’s a vestigial reflex related to the primate sounds.

In the elegantly titled 2008 applied acoustics paper, Scraping Sounds and Disgusting Noises, Cox suggests two other possibilities for our dislike of the genre: “The response may have arisen as a by-product of our language learning, on the other hand it might be an evolved response to avoid stimuli which are averse to hearing other sounds.”

But it seems we still need to scrape some more to find concrete answers. “The internet experiment reported in this paper cannot provide any evidence as to the validity or either of these suggestions, and examining these possibilities is left to future work,” he writes.