Our world is a noisy place. Everywhere we go there is a veritable cacophony of noise pervading our surroundings, ranging from the sound of civilization, with its factories, construction, airplanes, and myriad vehicles with their roaring engines and speaking their language of honks and beeps, to the natural sounds of the wind, animals, and the earth’s various activities. Even in the realm of things we cannot physically hear there is noise, with the atmosphere saturated by all manner of low-frequency sounds both artificial and natural, as well as the countless waves and transmissions that give us our radio, TV shows, satellite information, and cell phone usage. Yet even beyond this there seems to be something more creeping about in the background, some ill-defined and persistent noise that only some can hear and which remains unexplained.

What has come to be mostly referred to as simply “The Hum,” or sometimes “The Worldwide Hum,” is a blanket term for a series of mysterious, inexplicable auditory phenomena that has emerged all across the world, and which typically entails a low frequency, persistent bass droning or rumbling noise, heard both indoors and outdoors and with no readily identifiable source or origin. It has been described as sounding like different things by different people, but a common description is that it sounds rather like an idling truck or industrial fan, and can vary in intensity from a general low bass background grumble to an invasive, ear piercing symphony of noise, depending on the person and location. This hum is most typically reported from rural or sparsely populated areas, but not always, and it is usually most noticeable in the evening hours, although this also depends on the person hearing it.

It is difficult to track down just when the phenomenon started, but it has apparently been around since at least the 1940s, when hundreds of people in the London and Southampton areas of Great Britain complained of a noticeable drone, and probably since much earlier. The 1950s and 1960s also saw the hum become widely publicized in the news and entering the public consciousness with various other reports from all over Great Britain, and in the 1970s there was a veritable media circus over the odd, persistent sound in Bristol, England, where complaints flooded in when many residents reported hearing it. The phenomenon would continue in Great Britain into the 1980s, where it was widely heard by residents in Largs, Scotland, a coastal town about 31 km west of Glasgow.

The Hum made perhaps its most famous debut in North America in 1992, when people in and around the town of Taos, New Mexico, began to report the sound, which has since become known as the “Taos Hum” and is probably the most well-known location for the phenomenon. The Hum also appeared in the United States in Kokomo, Indiana, in 1999, where it seems to have had a particularly potent effect, allegedly causing various negative physical symptoms such as headaches, nausea, dizziness, fatigue, and joint pain, to the point that many who heard it purportedly moved away to escape it. An in-depth investigation into the source of the Kokomo Hum by the Board of Public Works and Safety could not determine exactly what caused it. In the years since, the Hum has gone on to be reported from numerous other locations from all over the world, in such far-flung places as Italy, Canada, Australia, New Zealand, and Mexico, among others, to the point where an attempt to chart the phenomena, called The World Hum Database and Mapping Project, was launched in 2012, containing a huge database of hum reports and locations all over the planet.

The hum phenomenon cannot be heard by everyone, and it has been estimated through studies in the U.S. and Great Britain that only about 2 percent of the population are actually susceptible to it, both male and female and usually those of middle age or older. For those who do hear it, often referred to as “Hummers,” the description of the hum is often very similar, and it is claimed that earplugs do nothing to stop the relentless drone or reduce its volume in any way. Although the description of the sound itself is mostly consistent, the situations in which these people can hear the sound can vary, for instance with some hearing it more often indoors while others are more prone to picking it up outdoors, and some hearing it more at night while others are affected only during the day. The volume and intensity of the Hum can vary between individuals as well, with some only faintly picking it up as an annoying but harmless static of sorts, while for others it can be absolutely blaring and some even reporting feeling it vibrate through their bodies or homes.

For the people who are very sensitive to the noise, it can supposedly be a deeply unsettling, life-altering experience; a nightmare in a sense. It can apparently cause a wealth of symptoms, ranging from ear pain, headaches, nosebleeds, and nausea, to more debilitating problems such as fainting or chronic pain in various parts of the body. It also allegedly alters emotional states, causes memory loss, impaired speech, and diminishes overall energy levels. The Hum has caused people to do drastic things, like sell their homes and move away, quit their jobs, spiral into depression, and in some extreme cases has even driven people to suicide. One sufferer named Hugh Witherington began to hear the Hum upon moving away from his home of London, England, to the quiet countryside of Hertfordshire, and has been continuously terrorized by it ever since, explaining it thus:

It sounded like a lorry had stopped outside my window and left its engine idling. No amount of exposure ever gets me used to it. It stops me from thinking, even now. I cannot accept it.

Another example of a sufferer whose life has been deeply affected by The Hum, 46-year-old Rosemarie Mann, of Romsey, England, claims that she is so plagued by the potent and nonstop noise that it has profoundly changed her life in the worst of ways. She says that it had dragged her down into depression, for which she now takes medication, diminished her will to live, and has strained her marriage. It is something she has to wrestle with every day, and she has said of the harrowing experience:

I can only describe it as a kind of torture. For the first few years I lost sleep, couldn’t concentrate and was unable to do anything. I was constantly in tears, which put a great strain on my husband. It has changed me from an active, creative person to a stifled, angry pessimist. The Hum still has a terrible draining effect. It is the invasiveness and relentlessness of the noise and having no understanding or control of it which makes it so distressing.

There have been numerous theories on what The Hum could be, ranging from the rational to the truly outlandish. One of the simplest explanations that has been offered is that these people are suffering from a fairly common condition called tinnitus, which is a perceived noise or ringing in the ears with no external cause and which can be caused by factors as varied as noise induced deafness, ear infections, head injuries, or mental conditions such as emotional stress or depression. The problem with this is that Hummers are adamant that the noise is produced externally, also saying that it is a much different sound than tinnitus, and furthermore the hum seems to be generally heard in clusters tied to certain locations.

Similar to this theory is that The Hum could be the result of various internal physical or mental causes which are causing some sort of auditory hallucinations, or perhaps it is caused by medication or toxins. The hum has also been speculated to perhaps be the result of sudden noises generated by our own inner ears, called “spontaneous otoacoustic emissions.” It has also been suggested that the hum is merely all in these people’s heads and that it is a combination of over-imagining and mass hysteria or mass delusion fueled by the Internet. In this scenario, these people are just imagining it all, or are having their senses and perceptions colored by what they have read about the mysterious Worldwide Hum.

There is also the widespread idea that The Hum is caused by some mechanical source, such as cooling towers, industrial plants, ventilator fans, generators, and so on. While this may be true in some cases, and has even been shown as such in some instances, in others The Hum has persisted even when such factors were eliminated, and additionally in many cases the sound has not been successfully tracked down to any particular mechanical source. Another manmade potential cause for The Hum put forward has been electrical grids or cell phone towers, but even if these are the origin in some more modern cases, cell towers were not around when the hum phenomenon started taking off. Also, even if the cause is somehow mechanical in nature it still does not explain why only a small percentage of human beings even seem to be affected by the hum, and to varying degrees.

Very Low Frequency (VLF) radio transmissions (between 3 kHz and 30 kHz), could also be the answer to the phenomenon, especially as it has been surmised that the human body can sometimes register electromagnetic waves as actual sounds. It could also be the result of any number of low or ultra-low frequency sounds or infrasound, those just on the threshold of human hearing, either human generated or by natural phenomena such as earthquakes or other seismic activity, and volcanic or tectonic plate activity, as well as pressure waves reverberating across the seafloor. Another natural source that has been proposed is that the sound is caused by the mating calls of certain species of fish, but in most cases any significant drone caused by this requires a boat hull to amplify it, and it has been argued that these sounds on their own would be insufficient to be a convincing candidate. With any of these explanations, we are still faced with the apparent fact that only some people can hear it.

If there is such a mundane cause for The Hum, then it seems fairly clear that whatever it is mostly likely stems from a combination of all of these, depending on the person, place, and the situation, with no one theory fitting every case. Of course with a phenomenon as mysterious and still largely unexplained as The Hum, there are certainly more far-out theories floating around as well. For some The Hum is indicative of a deep dark, government conspiracy complete with secret, shadowy experiments, mind-control devices, and cover-ups. Some have suggested that it is even a secret weapon utilizing focused ultra-low frequency waves and perched upon a satellite, which can beam down to target individuals or groups of people. For others it is the result of someone or something tunneling through the earth. There are also, of course, aliens. Why not? Still others claim that this is just something that originates in forces that currently lie outside of our understanding, but which we may someday fathom.

One of the problems posing an obstacle to coming to any real answers with the Worldwide Hum is that there have only been a handful of people who have ever tried to seriously study it, and those who have claimed to have experienced it are still largely dismissed and thought to be just “hearing things,” even as the number of reports and complaints from such people has been steadily increasing in recent years. Those who have looked into the problem with open eyes have been unable to come to a clear conclusion that can totally explain the breadth of the phenomenon. They simply don’t know what causes it or why it happens. It seems to be for now a strange phenomenon that is doomed to be just an anomaly that we may never fully understand, and that those who hear it will most likely just have to deal with it, to live with the incessant drone echoing through their head, possibly without ever knowing just exactly what it is they are hearing.

What is at the heart of the Worldwide Hum phenomena? Is this the result of artificial or natural frequencies or phenomena that some people are just more inclined to be sensitive to, or maybe some effect that we have yet to come to a clear understanding of? Is it some sort of radio waves or electromagnetic or sonic interference? Is it secret government experiments or weapons, aliens, or something more paranormal in nature? Perhaps at some point we will have more of an idea of what lies behind this strange background noise that seems to permeate some locations throughout the world and unravel its mysteries, but until then it will rumble on with its origin and purpose unknown.