NTNU Researchers Link Global Hum to Internal Physiological Tinnitus

For over five decades, thousands of people across the globe have reported hearing an incessant, low-frequency sound—often described as the hum of a distant engine or a rhythmic vibration. While the phenomenon gained widespread attention in the 1970s, particularly among residents of Bristol, England, it has remained a source of intense speculation and personal distress. Reports of the sound have since emerged from locations as diverse as the United Kingdom, the United States, Canada, Australia, New Zealand, Norway, and South Africa.

Investigating the Origins of the Global Hum

Because the sound is frequently reported as audible only in quiet indoor environments or at night, many sufferers initially suspected external sources such as industrial ventilation, heavy machinery, or electromagnetic radiation. These theories gained cultural traction, even inspiring the 2024 BBC drama The Listeners. However, repeated environmental inspections in affected areas have consistently failed to identify a singular, external noise source.

The study, published in PLOS ONE, sought to determine whether these individuals possessed heightened auditory sensitivity or if the sound originated within their own bodies.

We know that there are people who hear low-frequency sounds that can actually be measured, even if other people don’t hear them, but it’s not so easy to find the source of these sound waves, because it’s a struggle to localise low-frequency sounds. Markus Drexl, Professor at the Norwegian University of Science and Technology

Clinical Findings: Internal Signals vs. Auditory Sensitivity

The research team tested two primary hypotheses. First, they investigated whether the participants had an exceptional ability to perceive sounds in the low-frequency range. The results were largely negative, with only a very small minority of volunteers demonstrating a significantly higher sensitivity to low-frequency tones than the average person.

The second hypothesis, which the study identified as the most common cause, points to low-frequency tinnitus. Unlike high-pitched tinnitus, which is widely recognized, this variant involves the brain interpreting internal physiological signals—such as those generated by the ear—as external pulses. These signals are often mistaken for environmental noise, leading individuals to search their homes for non-existent machinery or faulty appliances.

Based on our results, although we haven’t ruled out cases of physical external sound sources, we suggest that subjective tinnitus in the low-frequency range is often the cause of hearing pulsations of low-frequency sound perceptions. Markus Drexl, Professor at the Norwegian University of Science and Technology

The Ongoing Challenge for Affected Individuals

While the study provides a significant breakthrough in understanding the mechanics of the “Hum,” it highlights a persistent gap in medical treatment. The condition shares characteristics with auditory issues experienced by high-profile musicians, including Dave Grohl, Brian Johnson, Pete Townshend, and the late Ozzy Osbourne, who have dealt with the consequences of long-term exposure to high-volume sound. Despite identifying the root cause, researchers acknowledge that there is currently no universal therapy for chronic low-frequency tinnitus.

For many, the findings offer a degree of validation. Digital tools like the Map and Database of the Global Hum have allowed thousands of people to register their experiences, confirming that the phenomenon is a widespread, albeit often isolating, experience. As medical research continues, the focus is shifting toward developing targeted treatments that can offer relief for those whose daily lives are disrupted by this persistent, invisible sound.