A mysterious low-frequency hum, which residents worldwide have complained about for decades, might not stem from external noise sources but rather from peculiarities within the auditory system itself. This is the conclusion reached by scientists at the Norwegian University of Science and Technology. Their findings were published in the journal PLOS One.
The phenomenon in question involves individuals perceiving a humming sound, akin to an engine running. These complaints most frequently arose during the night and indoors. Crucially, other people nearby would not detect any sound, and attempts to locate an external source of the noise were typically unsuccessful.
Such reports have been documented since the 1970s. Descriptions of a certain “hum” have emerged from residents of the UK, USA, Canada, Australia, and other nations.
The mystery of the “hum” unraveled
The researchers set out to determine if the phenomenon could be linked to heightened sensitivity to low frequencies. To do this, they examined 28 individuals who had reported experiencing these sensations. Scientific analysis revealed that the majority of participants possessed hearing comparable to the average, and no pronounced sensitivity to low-frequency sounds was detected.
Subsequently, the scientists explored an alternative theory. They investigated whether the sound source could originate within the inner ear and be connected to otoacoustic emissions—faint signals that individuals typically do not perceive. However, this hypothesis also proved unfounded.
According to the study’s authors, a portion of the enigmatic hum cases can be attributed to low-frequency tinnitus (a symptom associated with various pathologies — editorial note). In such a condition, a person hears a sound without an external source. This could manifest as a hum, buzzing, hissing, or other noises generated within the auditory system.
However, the researchers did not rule out the possibility that in specific instances, the “hum” might indeed have genuine external causes. Nevertheless, they suggested that many complaints could be associated with how the brain processes low-frequency signals.
Furthermore, the study’s authors emphasized that the perception of low frequencies and infrasound is less understood compared to the perception of high-pitched sounds. Consequently, this phenomenon warrants further scientific investigation.
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