In the US border town of Niagara Falls, residents accustomed to the soothing roar of the famous waterfalls recently discovered a much less pleasant sound: the "haunting hum" of bitcoin mining farms.

"I get four hours of sleep, maybe, because of that constant noise," said Elizabeth Lundy, an 80-year-old retired hairdresser. "I can hear the noise even through the storm windows."

On a sunny October morning, a mechanical whirring could be heard clearly on Lundy's front porch. The noise turned to a deafening din as one walked two blocks toward Buffalo Avenue where the US bitcoin miners operate.

Bitcoin mining farms have multiplied in the United States since China halted this activity in 2021. The United States is now emerging as a global leader in the industry.

Attracted by the cheap hydroelectric power available in Niagara Falls, Blockfusion took up residence at a former coal factory there in 2019, followed by US Bitcoin in 2020, which operates from a former sodium plant.

US Bitcoin installed hundreds of noisy fans outside, needed to cool the thousands of computer graphics cards that heat up as they solve the complex equations required to earn them cryptocurrency.

- 'A 747 jet' -

"It sounds like a 747 jet," said Frank Peller, a 70-year-old resident who lives in a brownstone more than a mile from this crypto mining operation.

"It's the loudest in the morning, at night and if there's high humidity and a breeze," he added.

He once could sit in his backyard and hear the roar of Niagara Falls more than two miles away. But now, "you can't hear it at all" and you can't avoid "the roar of bitcoin mining every day."

Bryan Maacks, who lives closer to Buffalo Avenue, described a "haunting, vibrating hum" -- a vexing throb that has run through his house day and night since last winter.

"It's very mentally daunting. It's like having a toothache for 24 hours a day every day," Maacks, 65, said.

He said he wears headphones all the time and uses a fan to block out the noise to get to sleep.

Maacks launched a petition and made a "US Bitcoin Stop the Noise" sign on the back of his red pickup truck, which he parked for several weeks in front of the company.

"The noise pollution of this industry is like nothing else that has been there," said Niagara Falls Mayor Robert Restaino in his office decorated with paintings of the famous waterfalls.

That's quite a statement in a city that embraced heavy industry for decades.

Faced with a flood of complaints, mainly regarding US Bitcoin, the mayor decreed a moratorium on any new mining activity in December 2021, then in early September set strict noise limits of 40 to 50 decibels near residential areas.

- 'Noise barrier' -

US Bitcoin said it's taking steps to address the problem.

"Immediately upon these concerns being flagged, we erected a plastic barrier," the company said in a statement to AFP.

"We also conducted acoustic studies and had plans drawn for a larger noise abatement wall" that was prevented from being built by the moratorium, the company said.

In the nearby town of North Tonawanda, the Canadian mining company Digihost, is also facing the ire of local residents, and has undertaken the construction of a soundproofing wall more than six meters (20 feet) high, at an estimated cost of several hundred thousand dollars, Mayor Austin Tylec said.

In Niagara Falls, City Hall ordered the closure of the two bitcoin farms in early October until they comply with new local statutes.

While both companies say they are cooperating with the city, only Blockfusion had shut down its processors by the end of October and reduced the number of fans running, with US Bitcoin's still running at full capacity, an AFP reporter found.

"If they continue to refuse to comply with our order to stop, then we'll have to be in court," Restaino said.

Such a legal battle already pits the bitcoin farm Red Dog Technologies against local authorities in Tennessee. Other complaints about noise pollution in the vicinity of computer centers have arisen from North Carolina to Pennsylvania.

"I'm going to be protesting till the hum is gone, basically, till I get the roar of the falls back because that's what I used to hear," Maacks said.

© Agence France-Presse