13 Unexplained Natural Sounds That Still Puzzle Scientists

13 Unexplained Natural Sounds That Still Puzzle Scientists

The natural world is full of surprising noises that defy easy explanation. From persistent low-frequency rumbles to baffling underwater booms and eerie nocturnal wails, these acoustic mysteries have attracted scientists, amateur recordists, and folklore alike. Below are 13 of the most intriguing unexplained environmental sounds, summaries of what was heard, and the main scientific and speculative explanations proposed so far.

1. The Hum

The Hum is a widespread, low-frequency droning reported in many countries. Those who hear it describe a constant, intrusive rumble with no clear external source; others nearby may not hear anything at all. Investigations have considered industrial noise, infrastructure, perceptual phenomena and electromagnetic effects, but no single cause has been universally accepted. For some sufferers, the Hum significantly affects sleep and concentration.

2. The Bloop

Recorded in 1997 by ocean monitoring networks, the Bloop was an extremely loud, low-frequency underwater sound that initially led to speculation about a gigantic unknown animal. Later analysis by NOAA found the acoustic signature consistent with icequake activity—large icebergs cracking and fracturing—making a glaciological origin the leading explanation. The episode remains a useful example of how mysterious sounds can inspire sensational theories before rigorous analysis clarifies them.

3. The Taos Hum

A specific instance of The Hum centered in Taos, New Mexico, where residents described a steady noise like distant diesel engines. The Taos Hum attracted formal studies and public attention, including inquiries that prompted scientific review. Hypotheses have included low-frequency electromagnetic fields, local industrial sources, and perceptual factors; none has achieved broad consensus.

4. Skyquakes

Skyquakes are brief, explosive booms heard as if coming from the sky—often likened to distant cannon fire or unusual thunder. Reports typically lack physical traces, which complicates analysis. Possible causes range from atmospheric phenomena and sonic booms to meteors and human activity, but inconsistent timing and descriptions mean skyquakes remain an open question.

5. The Upsweep

Recorded by the Pacific Marine Environmental Laboratory since 1991, the Upsweep consists of rising-pitch underwater sounds that recur seasonally. Scientists have tested biological and geological sources; volcanic activity in the general region is a candidate, though continuous volcanic sources have not been clearly identified. The Upsweep continues to intrigue oceanographers researching undersea soundscapes.

6. Aurora Crackles

Many observers of strong auroral displays report faint crackles or pops coincident with visible lights. Because auroras typically occur hundreds of kilometres above ground, the idea of audible auroral sounds challenges simple acoustic explanations. Recent hypotheses propose that local electromagnetic and atmospheric conditions might allow very faint, localized sounds to be perceived near the ground, but the phenomenon is still debated and requires more rigorous, repeatable recordings.

7. The Colossi of Memnon “Song”

Ancient visitors to the Colossi of Memnon in Egypt described a dawn “singing” or whistling from the statues for centuries until the sound ceased in antiquity. Modern acoustic studies suggest temperature-driven expansion and contraction of stone or structural effects of the statues’ composition could have produced the noise. While the phenomenon no longer occurs, historical accounts remain an intriguing blend of architecture, climate, and early acoustical observation.

8. The Whistle of the Northern Lights

Separate from reported auroral crackles, some eyewitnesses describe a soft, whistling accompaniment to the northern lights—especially where ambient noise is minimal. Proposed mechanisms mirror those for auroral crackles: localized electromagnetic interactions and ionospheric fluctuations that might generate transient sounds or sensations. Evidence is still limited and often anecdotal, so the whistle remains an unsettled claim.

9. The Forest Grove Sound

In 2016, residents of Forest Grove, Oregon, reported a piercing, high-pitched noise—compared to metal scraping or a failing brake—that moved through neighborhoods and resisted localization. Investigations considered industrial equipment, utilities, and other man-made sources but uncovered no definitive origin. The disturbance stopped as mysteriously as it began, leaving the event unexplained.

10. Subterranean Moans

Low groans and moans heard in areas with caves, karst terrain, or unstable geology are often attributed to natural processes such as shifting rock, groundwater flow, or minor seismic events. While geological explanations are plausible, the sounds’ irregularity, local variability, and the overlay of folklore sometimes make firm scientific attribution difficult.

11. The Seneca Guns

For centuries, people along parts of the U.S. East Coast have reported sudden, thunder-like booms—called the Seneca Guns—sounded like distant cannon fire. Theories include underwater gas releases, distant thunder or atmospheric ducting, and seismic activity, but the sporadic nature and lack of consistent data have prevented a single accepted explanation. The phenomenon has entered regional folklore and continues to be reported intermittently.

12. Midnight Roars of the Amazon

Indigenous and local accounts in parts of the Amazon describe ominous, very loud roars heard at night—so powerful they suggest an enormous unseen creature. Researchers have considered seismic origins, acoustic amplification by terrain and vegetation, or as-yet-unidentified biological sources, but modern field recordings have not conclusively captured the phenomenon. The reports highlight how remote environments still hold acoustic mysteries.

13. The Harbinger’s Howl

Reported in parts of Scandinavia, the Harbinger’s Howl is characterized as a distant, mournful wail or series of uncanny howls often linked in local tradition to approaching weather. Explanations range from wind-channelled acoustics in mountainous terrain to more folkloric interpretations. Scientific recordings have been attempted, but results are often ambiguous; the howl remains an evocative regional enigma.

Bottom line: Many of these sounds now have plausible scientific explanations (for example, icequakes for The Bloop) while others remain poorly documented or dependent on anecdotal reports. Continued field recording, careful acoustic analysis, and interdisciplinary study are essential to distinguish natural processes from human-made noise and perceptual phenomena.