The sound most people can't hear: 1 in 25 people are haunted by the 'Global Hum'. Are you one of them?

People across the world have complained of hearing a low-frequency sound with a mysterious source. Known as the Global Hum, this is not something everyone can hear. It is described as a distant idling diesel engine or a heavy drone by roughly 2% to 4% of the global population, who are the only ones who claim to hear it. Scientists have tried to record it, but have never been successful. Medical tests on people known as "Hearers" have ruled out any health conditions. The Global Hum remains a puzzle and unsolved to date. The University of Southampton and NOAA have studied it and tried to find what's causing the sound. Listeners say it is more than just a faint noise, but they can actually feel it manifesting itself physically in their bodies. It has caused sleepless nights, headaches and even psychological distress in some people. While the phenomenon was first recorded in the 1970s, a new surge of reports in New Jersey has scientists looking at modern data centres as the potential culprit.

Who hears it?

Observations over the years have shown that the majority of hearers are middle-aged and older adults with perfectly normal hearing. It gets louder in the quiet of the night, especially indoors, when it feels like a vibration. People complain of feeling nauseous and experiencing headaches.

Hotspots of the hum

Global Hum, as the name suggests, has been reported from various parts of the world. However, there are three places that have been dubbed the "hotspot" for this activity. The most famous is the Taos Hum, in New Mexico, USA. Residents were so distressed by a strange sound in the 90s that Congress launched an investigation. The Bristol Hum in the UK was one of the first instances of people hearing the sound. In the 1970s, hundreds of people complained of a rhythmic thrumming. The Windsor Hum in Ontario, Canada, is the third hotspot, although a few of the sounds were traced back to blast furnaces on Zug Island in Detroit, while others remain unexplainable.

Quick facts

Frequency: 10Hz to 80Hz

Percentage of Population: 2% - 4%

Top Theory: Microseismic ocean waves

Scientific theories on Global Hum

Scientists have proposed various theories to explain the Global Hum. Since one person can hear it and another right next to him won't, possibilities range from biological reasons to geophysical. One of the most common theories is linked to Earth. Microseismic activity inside our planet creates sounds which could be picked up by certain people with more sensitive auditory systems. When ocean waves collide with the seafloor, very low-frequency vibrations (around $0.01$ Hz to $0.5$ Hz) are generated that are too faint to be heard by the human ear. But some people can possibly hear these subtle sounds.

The second theory is that the hums could be coming from industries. Gas lines, electrical transformers, or large industrial cooling fans make noises that can travel through the ground for several kilometres. These low frequencies have very long wavelengths that help them pass through walls. In March this year, people in Vineland, New Jersey, complained of hearing mysterious humming sounds. Residents said that the constant low noise was coming from a massive data centre being built nearby, even though no direct link was found.

The biological factors linked to Otoacoustic Emissions state that some people's inner ear creates a faint hum, which might be perceived as external noise. The idea of tinnitus has also been floated, but it falls flat because it is a high-pitched ringing, while the Global Hum is a low-frequency sound.

Why does the Global Hum remain unsolved?

Figuring out the reason has been a problem because the Hum sits at the edge of human perception. Regular microphones fail to detect the faint noise, which also easily gets drowned out amidst other sounds. Besides, the Global Hum most likely does not have a single origin. It could be geological in one place, and industrial in another. Whatever it is, Hearers are sure that this invisible experience is real, even though the medical community and the general public have dismissed their assertions.