Study proposes two mechanisms for why only some people hear 'The Hum'

A study published in PLOS One proposes two mechanisms to explain why 2-4% of the global population reports hearing a persistent low-frequency hum that others cannot detect. Researchers led by Markus Drexl at the Norwegian University of Science and Technology tested 28 people who reported hearing the unexplained sound. They found evidence for two non-exclusive explanations: some hearers have unusually sharp sensitivity to externally generated low-frequency sound, while others may be perceiving faint sounds generated by their own inner ear as a normal by-product of cochlear amplification. The phenomenon, documented since the 1970s in Bristol, England, and later in Taos, New Mexico, Kokomo, Indiana, and other locations worldwide, varies widely in impact-some people barely notice it, others find it debilitating. Canadian teacher Glen MacPherson's World Hum Map and Database Project, launched in 2012, shows report clusters in densely populated areas, suggesting human-made infrastructure may contribute. The study adds a physiological dimension to what has largely been an environmental mystery.