The mysterious “global hum” has baffled scientists for years. Approximately four percent of people hear this consistent, low-pitched noise, but experts have struggled to determine the source.
Simon Payne of Cambridgeshire in the UK is one of the unlucky ones who can hear the hum.
“I have been desperate to get away from it, so I have stayed with friends – and even moved house,” he said .
Scientists have suggested many theories, but have not proven any of them- until now. It turns out, this elusive “global hum” has been coming from a volcano.
What is the “Global Hum”?
People who can hear this low-pitched humming sound report experiencing insomnia, headaches, and dizziness because of it.
A 2004 investigation by geoscientist David Deming revealed that people have been complaining about this humming sound since the 1970s. Deming, who is a hearer himself, was unable to find a source for the sound. His is one of the few formal studies that exist.
His report states that the hum has predominantly affected the United Kingdom, but reports of the sound in the US date back to the 1990s. The two most publicised locations have been Taos, New Mexico, and Kokomo, Indiana .
The mysterious nature of the sound, not surprisingly, attracted many conspiracy theorists and alien fanatics. This caused many mainstream scientists to stay away from it entirely.
In 2012, however, science teacher and former university lecturer, Glen MacPherson, heard the hum himself. He then decided to pick up where Deming left off, and try to find the source of the noise.
MacPherson created an interactive map that includes thousands of hearer’s descriptions of what they heard and where they were. He then recruited a global team of volunteers to investigate what could be causing the hum in various countries.
MacPherson set out to test the following four hypotheses:
1. Natural sources of sonic phenomena
Sounds resulting from volcanoes, for example, can travel unbelievable distances. These sounds can sometimes circle the Earth multiple times. Elizabeth Silber, a Canadian physicist and planetary scientist who investigated reports of a hum in Windsor, Canada, wasn’t too sure.
“There are many natural sources … such as aurorae, lightning, meteors, volcanoes, waterfalls and ocean waves. Yet none of these seem to be consistent with the manifestation of the Hum.” 
2. Urban noise pollution
A large proportion of hearers live in urban areas. This makes it possible, then, that the hum is simply some form of urban noise pollution. Deming’s work, however, ruled out this option. Most of his evidence suggested that the hum was not an acoustic sound.
“This is indicated by the simple fact that most people do not hear it,” he said .
3. Low-frequency radio signals
Deming thought that very low-frequency radio signals could be causing the global hum. Those signals are used around the world to communicate with submarines. Radio signals can cause a “microwave auditory effect”. This is when radiant energy interacts with soft tissue in the skull and stimulates the auditory nerve.
MacPherson tested Deming’s theory by building a black box to block out those frequencies, but the hum only grew louder.
4. No external source
MacPherson believes it is possible that there is some neurological element to the hum. This is because when you put multiple hum-hearers in the same room together, they will all match the hum to different acoustic frequencies.
“That never, ever happens with standard acoustic sources, of any frequency. It just simply never happens,” he said .
MacPherson has not yet been able to determine the source of this internal perception of sound.
The Global Hum: An Answer
Earlier this year, scientists finally solved the mystery. The culprit? A volcano.
New findings revealed that the rumblings of a magma-filled reservoir deep under the Indian Ocean were causing seismic hums that some people could hear around the world. A few months later, an underwater volcano was born off the coast of the island of Mayotte, between Madagascar and Mozambique.
In May 2018, earthquake-monitoring agencies from around the world detected thousands of earthquakes near Mayotte. Later that November, seismologists recorded seismic hums that lasted up to forty minutes.
According to Simone Cesca, a seismologist at the GFZ German Research Centre for Geosciences in Potsdam, Germany, the researchers found more than four hundred of these signals.
A New Volcano is Born
Finally, in 2019, French oceanographers found that a new volcano had been born. This volcano was massive, measuring 3.1 miles (5 kilometers) long and nearly a half a mile (0.8 kilometers) tall.
Other researchers suggest that the global hums are from not just the volcano alone, but from a shrinking magma chamber. This is evidenced by the fact that Mayotte has sunk and moved several inches since the earthquakes began.
The researchers describe two stages that caused the volcano, and subsequently, the hum:
- Magma from a reservoir flowed up diagonally until it reached the sea floor, causing an eruption below the ocean.
- The path this created allowed magma to travel out of the reservoir to the sea floor, where it built the volcano. This caused the area above the reservoir to weaken and sag, creating small faults and fractures. When earthquakes shook the area above the reservoir, Cesca said they caused “the resonance of the deep reservoir and generate[d] the peculiar, very long period signals,” .
So it seems that MacPherson was onto something with his first theory- that the hum was from a natural source. While finally knowing where the hum is coming from may be satisfying, it doesn’t necessarily provide relief to those who hear it. Helping those individuals may be the next puzzle to solve.