Theories about the cause of the phenomenon The Hum abound, from acoustic pollution originating from human sources, to sounds that nature itself makes. Or that the ear itself produces the humming sound. (Credit: Idun Haugan, NTNU)
Is That Mysterious Low Hum Actually a Form of Tinnitus? New Study Says It May Be
In A Nutshell
- An estimated 2–4% of people report hearing a persistent low-frequency hum that others around them cannot detect.
- A new study tested two leading explanations and found little support for either: most hum hearers don’t have unusually sensitive hearing, and no low-frequency inner-ear sounds were detected.
- Researchers point to low-frequency tinnitus as the most plausible explanation for many cases, though it was not directly tested and external sound sources remain possible in some individuals.
- 86% of participants described the hum as stressful, and 68% said family members could not hear it.
For some people, a relentless low drone fills the background of daily life, like a diesel engine idling just out of sight. It persists through quiet rooms, through the night, through years of frustration. Neighbors don’t hear it. Family members don’t hear it. New research into the so-called “hum phenomenon” now points toward a conclusion that may surprise those who have long blamed the outside world: for many people who experience it, the sound may not be coming from outside at all.
Between 2% and 4% of the general population reports hearing an almost constant low-frequency sound, often described as pulsing, rumbling, or throbbing. It has made headlines in Oslo, Norway; Darmstadt, Germany; and Windsor, Canada, where clusters of people came forward reporting the same maddening noise. Theories have ranged from industrial equipment to underground pipes to government activity. But researchers publishing in PLOS ONE tested two scientifically plausible explanations and found little support for either as a broad explanation, pointing instead toward a low-frequency form of tinnitus, the condition where the auditory system generates phantom sounds with no external source.
Tinnitus is most commonly associated with high-pitched ringing after a loud concert. But the research team argues it can also occur at very low frequencies, and for many hum hearers, that internal misfiring of the auditory system is the most plausible culprit.
Low-Frequency Hum Hearers Report Stress, Social Disconnect
Researchers recruited 28 people who reported hearing a low-frequency hum, with a median age of 53.5 years, through a social media group where hum sufferers organized to share their experiences, comparing them against control groups totaling 38 younger adults with normal hearing.
Participants were first asked to match the pitch of what they heard to a tone adjustable at home using a free online tool. Among the 23 who completed this, the median frequency reported was 50 Hz, a very low pitch close to the electrical hum of power lines and appliances, where most people need much louder sounds to notice anything at all. Five participants said their sound was too complex to match to a single tone.
A questionnaire revealed how much the experience weighed on daily life. A full 86% described the hum as stressful, and 68% said family members could not hear it. About 39% also reported high-pitched ringing, what most people recognize as typical tinnitus. And 68% said the sound had no clear direction, suggesting it didn’t feel like it was coming from outside.
Low-Frequency Hum Study Finds No Evidence of ‘Super Hearing’
One leading theory holds that certain people have extraordinarily sensitive low-frequency hearing, picking up real environmental sounds that most ears can’t register. To test this, researchers mapped precisely how loud a low-frequency sound needed to be before each participant could detect it, using methods more precise than standard hearing tests.
Results offered little support for the super-hearing theory. Most hum hearers, specifically 89% of measured thresholds, fell within the normal range of hearing sensitivity at low frequencies, comparable to the control groups. Only two participants showed sensitivity unusual enough to plausibly explain picking up real sounds others would miss.
Hearing sensitivity can spike and dip sharply across very narrow frequency ranges, a documented quirk where someone might be unusually sensitive at one exact pitch but not a few tones away. These fine-grained variations appeared in both the hum-hearing and control groups, making them an unlikely unique explanation.
No Low-Frequency Inner-Ear Sounds Found in Hum Hearers
A second hypothesis was more unusual: could hum hearers be listening to sounds their own inner ears produce? As part of normal function, the inner ear actively generates faint sounds. Roughly half the population produces these measurable sounds, though most people never perceive them because the brain filters them out.
Researchers tested whether some participants might be producing inner-ear sounds at unusually low frequencies and actually hearing them, using a dual-microphone probe designed to improve detection at very low frequencies.
No low-frequency inner-ear sounds were found. All sounds detected in both groups ranged from roughly 861 Hz to 4,637 Hz, far above the 50 Hz range where participants reported hearing the hum. That explanation, the researchers concluded, appears unlikely.
Low-Frequency Tinnitus Emerges as Most Plausible Explanation
With those two explanations finding little support, the research team pointed to a third possibility not directly tested here but fitting the pattern: low-frequency tinnitus. A phantom sound generated by the auditory system itself, with no external source, could account for what many hum hearers experience, particularly those with normal hearing thresholds and no identifiable outside source.
That conclusion doesn’t make the experience less real or less disruptive. Researchers do not dismiss the possibility that some individuals are genuinely detecting real sound sources others cannot hear. A small number of participants showed sensitivity unusual enough to make that plausible, and the team explicitly stated external sources cannot be ruled out.
For many, though, the evidence points inward. A hum that has driven people to petition local governments and move homes may often be a product of the same auditory system that produces the high-pitched ringing millions recognize as tinnitus, just pitched so low it sounds like the world itself is rumbling.
Disclaimer: This article is based on a peer-reviewed study and is intended for informational purposes only. It does not constitute medical advice. If you are experiencing persistent sounds, ringing, or other auditory symptoms, consult a qualified healthcare professional.
Paper Notes
Limitations
Enrolled participants were recruited through a self-organized social media group dedicated to the hum phenomenon, introducing potential selection bias. Frequency matching was conducted at home using consumer-grade equipment rather than in a controlled lab, which the authors acknowledge is less precise. Low-frequency hearing threshold measurements were limited to a narrow range centered on each participant’s self-reported pitch, limiting broader conclusions about sensitivity. Control groups were notably younger, with median ages of 24 and 22 years compared to 53.5 years for hum hearers, which may affect comparisons. Authors also note that the absence of detectable low-frequency inner-ear sounds does not definitively rule out their existence, only that current measurement technology could not detect them.
Funding and Disclosures
Authors received no specific funding for this work, as stated in the paper. One author is a member and administrator of the social media group from which participants were recruited but was not involved in the recruiting procedure. This potential conflict of interest is disclosed in the published paper.
Publication Details
Authors: Bonifaz Baumann, Andrej Voss, Carlos Jurado, and Markus Drexl. Baumann and Drexl are affiliated with the German Center for Vertigo and Balance Disorders, Grosshadern Medical Centre, University of Munich, Munich, Germany. Jurado and Drexl are also affiliated with the Department of Neuromedicine and Movement Science, Norwegian University of Science and Technology, Trondheim, Norway. Voss is affiliated with the Technical University of Munich, Munich Institute of Biomedical Engineering, Garching, Germany. | Journal: PLOS ONE | Paper Title: “On the potential sources of a low-frequency sound percept that only a few can perceive” | Published: March 27, 2026 | DOI: 10.1371/journal.pone.0326818
