Understanding the Mysterious Hum That Tortures a Select Few

What is the mysterious phenomenon known as “the hum?” Those who can hear it describe it as a low-frequency, rumbling sound, much like a hefty diesel truck idling nearby. Hearing protection doesn’t seem to help, and it’s often worse at night. Estimates vary, but perhaps somewhere between two and five percent of the world’s population has heard the hum. Most people can’t pick up on it at all, which frustrates those who can. “When nobody else can hear it, you think you are going nuts, and it just wears you down,” one hum-hearer in Cambridgeshire, England told the Guardian.