It's just the concept that unfamiliar ambient noises can become very grating to some people. Someone used to a particular fan might struggle with the sound of a different one. Someone used to the sound of a CRT TV might ignore it, while other people can't. Likewise, someone not used to silence can be uncomfortable with the lack of stimulus. It's a common aspect of sensory processing abnormalities, such as autism. It's well documented and entirely reasonable. Just because it's not a standalone disorder doesn't make it fake.