The Frequency Was Still There
An Update on the Creve Coeur Aeolian Resonance
When I first wrote about the sound I remembered from Creve Coeur, I was working almost entirely from memory. It was a distant, hollow tone that seemed to come through the woods at night. It was breathy rather than sharp, continuous rather than intermittent, and strangely difficult to locate. It reminded me of air moving across the mouth of a bottle, but enormous and far away. As if the landscape itself had found a note and held it.
My mother remembers it too, which told me that it was never solely an isolated childhood memory. Still, memory is imperfect. I could describe the sound, investigate the old Lake Erie Coal Company mine, compare maps, and consider everything from industrial machinery to temperature inversions, but I could not play the original sound for anyone.
I have started calling it the Creve Coeur Aeolian Resonance. “Aeolian” describes a sound created when moving air causes something to vibrate, like wind passing across a wire, opening, bridge, or hollow structure. It does not identify the source. It describes the quality that has remained consistent in my memory: air becoming tone.
Since that first post, the investigation has changed considerably.
Reconstructing a Memory
I began by trying to build the sound from scratch using the Garage Band app. This involved an unreasonable number of audio experiments. I often made comments such as “It needs less tornado siren,” “Make it more hollow,” “It sounds too close, it needs more distance,” and “It’s supposed to sound like someone learning to whistle who is producing more air than tone.” I tested different pitches, octaves, combinations, pulsing patterns, and layers of airy noise.
The closest reconstruction was not a single clean note. It needed several tones beneath an aeolian layer. A faint, breathy texture that prevented the result from sounding like a test tone, train, or industrial alarm. Earlier experiments centered on combinations near 312, 454, 520, and 794 hertz. The exact mixture changed as I listened, but the process helped narrow the central pitch I had been trying to match with my voice.
The Sound Across From the Mall
At around 9 p.m. on September 24, 2026, I heard a sustained outdoor tone from my home close by The Shops at Mission Viejo in and the surrounding businesses right here in California. I may also have heard it briefly two evenings earlier. It was not audible indoors, but outside it had the same frustrating ability to become more noticeable once other nearby sounds drew my attention toward it.
This was not an exact match for the Creve Coeur Aeolian Resonance. It sounded more plainly mechanical: airy, machine-like, and slightly fluctuating rather than like one perfectly fixed test tone. The recording showed a sustained component around 508-512 hertz.
Its location made ordinary commercial machinery an immediate possibility. Rooftop HVAC equipment, restaurant exhaust systems, refrigeration compressors, loading-dock machinery, service equipment, or nearby hospital infrastructure could all plausibly create a continuous tone in that environment. Nighttime atmospheric conditions could then allow it to travel farther or sound more prominent than it would during the day.
That recording was useful because it demonstrated how a distant mechanical source can acquire the same disembodied quality that made the Illinois sound so difficult to place. It also gave me another warning: two sounds can resemble each other without sharing either a location or a source.
Then something even more unexpected happened: I heard a closer match at my mother’s house in Ladera Ranch, California.
A Modern Recording
I managed to capture a sound in Ladera Ranch, CA in two recordings, one indoors and one outdoors. They were messy recordings. There were mice squeaking, water-bottle noises, wind, and the ordinary mechanical background of a house. But the resonance was present long enough to analyze.
The outdoor recording contained prominent components around 409.8, 470.6, 525.2, and 941.5 hertz.
This does not mean the California sounds and the Creve Coeur sound all share a source. The Ladera Ranch recording may represent air conditioning, another mechanical system, or a structure resonating nearby. What it gave me was something more limited but still useful: a measurable sound that my ear recognized as belonging to the same general family.
Most importantly, the strongest component was close to 410 hertz, the range I had repeatedly circled while reconstructing the sound from memory.
That was interesting. It was not yet evidence from Illinois.
The Video I Forgot I Had
Then I remembered that I archive nearly everything.
While searching through old TikTok videos for something unrelated, I found a video recorded in Illinois in 2021, during the second period of my life when I lived in the Creve Coeur area. Wind and conversation dominate the recording, followed by an abrupt explosion of music at the end by which I edited out, but there is a faint tonal trace underneath the foreground noise.
Audio analysis found a narrow component near 411.8 hertz. That is only about two hertz above the 409.8-hertz component in the modern Ladera Ranch recording.
There are important limitations. Speech can create temporary harmonics in this frequency range. The video did have distant hard to hear speech, and the old recording is short, compressed, windy, contains sounds of rustling leaves, and not remotely controlled. It does not preserve the full layered resonance clearly enough to declare the mystery solved. A stronger intermittent area around 600–606 hertz may also overlap with speech.
But the video matters for another reason: I know exactly where it was recorded.
Brady Park, 2021
The video was filmed in Brady Park, beside the wooded Coal Creek corridor in Creve Coeur.
That location places the recording within the same broader landscape I have been investigating: wooded ground, creek drainage, mapped manholes or access structures, and the wider area affected by historic underground mining. Several mapped features sit within a few hundred meters, while other suspected or documented mine-related features lie farther along the same connected corridor.
The map does not prove that a mine shaft, drainage structure, bridge, or underground opening produced the sound. Distance on a map cannot establish an acoustic pathway, and some historical mine locations may themselves be offset. The geography does, however, establish that this was not a video recorded somewhere vaguely in Illinois. It came from the actual wooded Creve Coeur landscape associated with the sound.
The date changes my understanding of the phenomenon too. For a while, I treated the Creve Coeur Aeolian Resonance primarily as something from my childhood. When I returned to Illinois and lived at the Gerber house, I did not hear it there. I could have interpreted that absence as evidence that the sound no longer existed.
The 2021 Brady Park video shows otherwise. The sound, or at minimum the same tonal component, was still present during my second period living there. It simply was not audible from the Gerber house. That turns a question of “when” into a question of “where”.
The sound may have depended on location, terrain, wind direction, atmospheric conditions, distance from its source, or the way particular structures carried and filtered it. A sound can exist within a landscape without being audible everywhere in that landscape.
What Could Produce It?
The closest real-world comparisons I have found remain industrial blowers, large air ducts, HVAC return vents, and structures that produce aeolian tones in wind. The way bridges can “sing” is especially relevant: wind interacting with rails, slats, cables, gaps, or other repeating structural elements can create sustained tones that travel surprising distances.
Recordings from industrial sites in the Peoria area have also contained similar hollow, airy qualities. They are useful comparisons, not proof of origin. Alarms, emergency equipment, fans, vents, and other machinery can overlap acoustically, and a similar sound does not automatically identify the same mechanism.
The old Lake Erie mine remains part of the investigation because of its underground workings, former air shafts, altered surface features, and proximity to the landscape where the sound was remembered. Mine airflow or a surface opening behaving like a resonant cavity is plausible. It is not established.
My current list of possibilities includes:
● industrial fans, blowers, or ventilation systems;
● airflow through ducts, culverts, manholes, or other openings;
● aeolian resonance from a bridge, railing, cable, or similar structure;
● a distant mechanical source carried unusually well by cold, stable air;
● airflow interacting with a mine-related opening or underground cavity;
● or several of these factors acting together.
Temperature inversions may be part of the explanation even if they were not the source. A stable layer of cold nighttime air can bend distant sound back toward the ground, allowing industrial or transportation noise to travel farther and seem directionless. That could help explain why the resonance felt both distant and everywhere at once.
What Has Actually Changed
I still cannot identify the source of the Creve Coeur Aeolian Resonance.
What I can say now is more substantial than what I could say before:
● My mother also remembers the sound.
● I was able to reconstruct its general pitch and aeolian character from memory.
● A modern sound that my ear recognized contained a strong component near 409.8 hertz.
● An archived 2021 recording from Brady Park contains a faint component near 411.8 hertz.
● The 2021 date indicates that the phenomenon persisted into my second period living in Illinois, even though I could not hear it from the Gerber house.
● The confirmed recording location lies inside the same wooded Creve Coeur corridor central to the investigation.
None of those facts identifies the machine, opening, bridge, shaft, or atmospheric condition responsible. Together, however, they move the story beyond an isolated memory.
I went looking for the source of a sound I remembered. Instead, years later and thousands of miles away, I found its frequency waiting inside a video I had forgotten existed.
The source is still somewhere beyond the edge of what I can prove.
But the frequency was still there.
