McCalla is an unincorporated community on the southwestern edge of the Birmingham metropolitan area, straddling Jefferson and Tuscaloosa counties in Alabama. In the spring of 2011 it briefly joined a list of places, from Bristol to Taos to Windsor, whose residents hear a sound that nobody can find.
What happened
In the second week of May 2011 the Birmingham television station WBRC reported that people in the Loveless Park neighborhood had been hearing a constant hum for about a week. Charles Cleckler, who first noticed it, said it had risen and fallen at the start and then settled into a steady buzz; neighbors compared it to a helicopter hovering out of sight, to cicadas, or to sirens a long way off. Cleckler and others walked the streets and the surrounding woods looking for a source and found that the sound seemed to move: whichever way they went, it came from somewhere else. The one clue was timing. The hum had begun at about the moment electricity was restored after the tornadoes that had cut power across the state at the end of April. No utility or agency was reported to have investigated, no answer was ever published, and the McCalla hum passed into the record as one more unexplained case.
The investigation
McCalla had no study of its own, but the phenomenon it belongs to has had several. Complaints of a low, throbbing or droning noise, heard mostly indoors and at night and usually by only a few people in a household, were documented in Bristol, England, from the late 1960s, where some 800 people eventually reported it and traffic and round-the-clock factories were blamed. In Taos, New Mexico, residents began reporting a rumble in the spring of 1991, and in the summer of 1993 a team from the University of New Mexico, Sandia and Los Alamos National Laboratories and the Air Force’s Phillips Laboratory set up acoustic, seismic, electric and magnetic sensors around the town. Hearers had matched the sound to tones between 30 and 100 hertz; the instruments, able to detect airborne sound far below the threshold of hearing, found nothing in that range above background. The lead investigator, mechanical engineer Joe Mullins, reported that no signal matched the descriptions and turned his attention to the hearing of the hearers themselves.
Windsor, Ontario, produced the opposite result. From 2011 residents of the city’s west end and of LaSalle reported a rumble that rattled windows, and Canada’s foreign affairs department funded Colin Novak of the University of Windsor and colleagues at Western University to monitor it. Their 2014 report confirmed that the hum was a real, measurable sound and identified the blast furnaces on Zug Island, a steel-making site in River Rouge, Michigan, as the only plausible emitter. The final report, released in 2021, kept that conclusion; the American side was never opened to the researchers, and by then the hum was being heard less often.
The explanations
Acoustician Geoff Leventhall, who has worked on low-frequency noise complaints in Britain for decades, found in a 2003 review that about two percent of people in an affected area hear a hum, that most are between 55 and 70, and that most have normal hearing on testing, which separates the hum from ordinary tinnitus. In a minority of cases he and others have found a machine, including a neighbor’s central-heating plant, a Chrysler plant in Kokomo, Indiana, and the furnaces at Zug Island. For the rest, proposals range from microseisms stirred by ocean waves to very-low-frequency radio transmissions, a hypothesis advanced by geoscientist David Deming and pursued by Glen MacPherson of the University of British Columbia, whose World Hum Map and Database had gathered some 10,000 reports by 2016. None of the non-industrial explanations has been tested to a conclusion. Mass hysteria has fallen out of favor, since most hearers search out the subject only after months of hearing the sound alone.
Where it stands
The McCalla hum was never traced, and its link to restored power lines, transformers or some nearby industrial plant remains a guess. The broader picture is a mixture: some hums are machines at the edge of hearing, found when someone pays for the instruments, and some are heard in places where the instruments find nothing. For the people in Loveless Park, as in Taos, the sound was real enough to keep them awake.