Spontaneous Otoacoustic Emissions — Could the Hum Come From Inside the Ear?

One of the most intriguing explanations for the Hum involves spontaneous otoacoustic emissions (SOAEs) — sounds generated by the inner ear itself without any external stimulus. The human cochlea contains thousands of outer hair cells that actively amplify incoming sound waves. In some individuals, these cells can spontaneously vibrate at specific frequencies, generating faint tones that the person perceives as real external sound. SOAEs are measurable with sensitive microphones placed in the ear canal and are more common than generally realized — they occur in roughly 30-40% of the population, though most people are unaware of them. Researchers have proposed that in certain individuals, SOAEs at low frequencies could be perceived as a persistent hum, particularly in quiet environments where there is no masking background noise. This would explain the Hum's most puzzling features: its selective audibility (only certain people's ears generate the emissions), its apparent increase in quiet environments, and its resistance to acoustic shielding. However, SOAE testing of confirmed Hum sufferers has not consistently demonstrated low-frequency emissions, leaving the hypothesis promising but unproven.