People who listened to a series of 74 recordings while having their brain activity measured by an MRI scanner rated the sound of a fork on a glass as the second worst noise, followed by chalk on a blackboard.

The scans revealed that unpleasant sounds provoked a stronger response in the brain pleasant ones such as the noise of blubbing water.

While sounds are processed in the brain's auditory cortex, uncomfortable noises activate the amygdala, a separate brain region which processes emotions.

When we hear sounds like nails on a blackboard – another of the worst-rated recordings – the amygdala takes charge of activity in the auditory cortex, making us more sensitive to the noise.