A mysterious low, droning sound has been reported for years by people in different parts of the world, often with the odd detail that nobody nearby can hear it.
Usually referred to as “The Hum”, the phenomenon has long been treated as one of those enduring mysteries that refuses to go away. It has prompted speculation for decades, with ideas ranging from environmental noise to the possibility that some listeners are simply more attuned to certain frequencies than others.
Fresh research now suggests that, in many cases, the explanation may not be out in the environment at all.
A study published in PLOS One in March 2026 and led by auditory scientist Bonifaz Baumann from the German Center for Vertigo and Balance Disorders (DSGZ) suggests that many people reporting The Hum may actually be experiencing a lesser-recognised type of low-frequency tinnitus.
That does not necessarily solve every case filed under the same label, but it does point to the auditory system itself as a likely source for a large share of reports.
“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,” said neuroscientist Markus Drexl of DSGZ and the Norwegian University of Science and Technology.
The Hum first gained wider attention in the 1970s after people in Bristol, England, described hearing a constant low-frequency noise, roughly around 50 Hertz.
Since then, comparable accounts have emerged in countries including Australia and New Zealand, as well as in a number of places across North America and Europe.
Those affected commonly describe the sound as a hum, rumble or drone. For some, it seems tied to certain settings, appearing at home late at night yet disappearing completely in a different environment the next day.
Attempts to identify a single cause have repeatedly run into problems. Some inquiries have detected nothing obvious, while others have uncovered possible sound sources that still did not fully match what sufferers said they were hearing.
“We know that there are people who hear low-frequency sounds that can actually be measured, even if other people don’t hear them,” Drexl explained.
“But it’s not so easy to find the source of these sound waves, because it’s a struggle to localise low-frequency sounds.”
Instead of focusing only on outside noise, the researchers chose to examine the people hearing the phenomenon.
Using a social media recruitment campaign, they enrolled 28 volunteers who said they experienced unexplained low-frequency sounds. The team then set out to test two of the most common explanations.
One idea was that people who notice The Hum may have unusually strong hearing at very low frequencies.
The other was that they could be perceiving sounds generated within their own bodies, specifically otoacoustic emissions. These are faint sounds produced by hair cells in the cochlea as part of normal inner-ear function, though they are typically too quiet to notice.
Participants first underwent hearing tests focused on lower frequencies. With the exception of two people, the group showed broadly normal sensitivity in that range, suggesting superior low-frequency hearing is unlikely to explain most reports.
“Even though the group we tested was small, it still means that the hypothesis of having especially good hearing for low-frequency sounds does not hold for most people,” said Drexl.
The team also checked for otoacoustic emissions by placing very small microphones into the ear canal, a standard method used to assess ear function.
Those results also failed to reveal anything out of the ordinary. That, the researchers say, supports the possibility that for some individuals The Hum is a subjective auditory perception rather than a sound that can be externally detected.
That leaves tinnitus as a strong candidate. Although the condition is often linked with ringing or high-pitched tones, it can also occur at much lower frequencies, which researchers believe may account for some experiences grouped under The Hum.
“While not directly tested in this study, low-frequency tinnitus might serve as a good explanation for many, but not all, cases,” the researchers concluded.
The PLOS One paper notes that low-frequency sound perceptions appear to affect only a small slice of the population, with earlier estimates placing the figure at around 2% to 4%. It also makes clear that The Hum is probably not a single phenomenon with one universal cause. In some cases, external sound sources may still be involved; in others, the source may be internal.
Importantly, classifying some instances of The Hum as tinnitus does not make them any less real. Tinnitus is a recognised medical condition involving the perception of sound without an identifiable outside source, and it is thought to relate to the brain’s hearing and sound-processing systems.
Researchers are still working to understand its full cause, and there is no definitive cure at present. Even so, there are established ways to help people cope with it, and further study continues.
For people who hear The Hum, this distinction matters. If the sound is being generated internally in some cases, identifying it as a form of tinnitus could help connect sufferers with support, management tools and treatment approaches that might previously have been overlooked.
The research has been published in the journal PLOS One.