Activists have done their own sleuthing.
Over six years, Mike Provost of Windsor, who helps run the Facebook page, has amassed more than 4,000 pages of daily observations about the duration, intensity and characteristics of the sound and the weather conditions at the time.
He said he had had to fend off skeptics and theorists who believe that the hum is related to secret tunneling, U.F.O.s or covert government operations.
Mr. Provost, a retired insurance salesman, said his work was a blend of obsession and hobby. “I’ve got to keep going,” he said in a phone interview. “I’m not going to quit this.”
The hum is not limited to Windsor, a city of about 220,000 people on the Detroit River. Mr. Provost said he had received reports from McGregor, Ontario, 20 miles to the south, and from east of Cleveland, about 90 miles away.
Tracey Ramsey, a member of the Canadian House of Commons, said in a phone interview that she regularly gets calls from constituents about the health effects of the hum. Residents have complained of headaches, sleeplessness, irritability and depression, among other symptoms.
“It’s something they are desperate for an answer to,” she said.
Tracing the noise’s origins is complicated by who hears it, and when and where.
Tim Carpenter, a retired consulting engineer who specialized in geotechnical engineering and machine vibrations and is an administrator of the Facebook page, said not everyone can hear it.
“It’s as if you had a fire hose moving back and forth and the people who have the water falling on them hear the noise, and if you’re outside that stream, you don’t hear the noise,” he said.
Researchers have found no trends related to gender or age for the “hearers.”
Dr. Darius Kohan, the director of otology and neurotology at Lenox Hill Hospital and Manhattan Eye, Ear and Throat Hospital, said that the low-frequency hum was unlikely to cause long-term hearing damage but that it could be as debilitating as tinnitus, a persistent ringing in the ears.
Scott Barton, an assistant professor of music at Worcester Polytechnic Institute in Massachusetts, said in a phone interview that infrasound, which is below 20 hertz, can create a sense of unease because it is unintelligible to human hearing but still detectable. While it is possible to be accustomed to certain noises (the hum of an air-conditioner, for example), this low-frequency noise is challenging because it has been so inconsistent, he said.
Seeking intervention by government regulators for the hum is difficult because regulations typically address decibel levels that can lead to hearing loss or damage, not those that can affect quality of life, Rebecca Smith, a sound engineer and doctoral student at the University of Michigan in Ann Arbor, who researches urban noise, wrote in an email.
“Think about the sound of a dog barking,” she said. “It doesn’t need to be loud enough to physically damage you to be really annoying and distracting.”
The University of Windsor report said the hum’s likely source was blast furnace operations on Zug Island on the Detroit River, which is densely packed with manufacturing. Activists complained that United States Steel, which operates the furnaces, has been uncooperative and secretive. A company spokeswoman did not respond to requests for comment.
A principal investigator on the study, Professor Colin Novak, told CBC News in 2014 that researchers needed more time and cooperation from the American authorities to pinpoint the source. “It’s like chasing a ghost,” he said.
Hums similar to Windsor’s have been reported in at least a dozen communities worldwide, including in Australia, England and Scotland, the study said. In the United States, high-profile hums have been reported in Taos, N.M., and Kokomo, Ind.
Researchers studied the Taos hum in 1993 but did not pinpoint a source. Karina Armijo, the town’s director of marketing and tourism, said in a telephone interview that complaints had subsided.
“I have never heard the Taos hum, but I’ve heard stories of the Taos hum,” she said. “There’s not been a lot of buzz about it in the last few years.”
A 2003 study in Kokomo by the acoustics and vibration consulting company Acentech prompted two industrial plants to install silencing equipment, providing relief to some residents but not all, a 2008 paper about the study said.
“In fact, one affected resident had become so disturbed that she moved more than 700 miles away to relieve her symptoms,” it said.
Mr. Carpenter said it was possible a major source of the Windsor hum could be eliminated and other mechanical sources would replace it, entering the “heard spectrum.”
“It’s possible that no matter what is done to relieve or attenuate the noise, it might never be enough,” he said.