CLINTONVILLE, Wis. — It was a quiet night last Sunday when the sounds began, and some residents have barely slept since.
Police in Clintonville, Wis., have received hundreds of calls this week from people awakened by noises they said seem to be coming from under the earth. At times, they said, it was like someone banging on the pipes in the basement, while at other times it was so loud windows rattled and the ground jolted.
City officials in Clintonville, a small town about an hour west of Green Bay, believe that there is no physical threat to residents and said no major damage has occurred to property. But night after night of the same quakelike episodes have inspired an obsession — driven by fear and fascination — to pinpoint the cause.
But almost a week after it started, there is still no complete explanation for why Clintonville, population about 4,600, is booming.
“People are obviously frustrated and would like to have some answers,” said Lisa Kuss, the city administrator.
The first tremors started about 9:30 p.m. Sunday. City officials, who now believe the noise to be a geological anomaly, said they first got wind of the problem about four hours later, after a louder series of “events” woke at least 150 people in the early morning.
“You got these big concussion booms like you’re in the middle of fireworks,” said Robert Ptacek, 49, who first thought the sound was someone trying to break into his house. “It was one time over there and the next time it was this way. It was coming from all over. Some of them more rapid, some of them five or six minutes apart, and then it would die.”
Verda Schultz, 47, thought someone was slamming car doors outside her house, but when she got up to yell at the person, she noticed that all the people in her neighborhood were already gathering on the street in their pajamas.
“There’s something radically wrong with this earth,” she said, noting that her horses and dog have been acting oddly for days.
Experts and area officials think they know what it is not.
That f irst night, they checked a nearby electrical substation but found no problems. Utility employees walked up and down neighborhood streets testing gas levels in the sewers, finding nothing unusual. The city has since looked for changes in the water pressure, tested methane levels at the local landfill, contacted the military about any exercises in the area and investigated nearby construction, industrial and mining activities — and come up with nothing.
Another possible explanation emerged Thursday, when officials said seismic monitors had noted a microearthquake — a magnitude of 1.5, and very rare for the region — just after midnight Tuesday that may have been responsible for some of the sounds.
The booms appeared to be localized in one small section on the north end of town, just east of Main Street. Some neighbors only blocks away from where people reported the disturbance said they heard and felt nothing.
“Microearthquakes in general happen all the time, all over the world, but we’ve never had one specifically detected in Wisconsin, especially a whole series of them like what we have been seeing going on in Clintonville,” said Harold Tobin, a professor of geoscience at the University of Wisconsin-Madison, who has been helping to diagnose the mysterious pounding.
“But people haven’t necessarily looked very hard for them,” he added. “It’s only because of the publicity that seismologists went looking for such a small needle in a haystack.”
Unexplained earthly noises, although odd, are not entirely unheard of. Tobin has been flooded with e-mails from across the country. But rarely does such thumping reoccur on multiple nights.
Residents of Windsor, Ontario, however, have been bothered on and off for more than a year by a low hum — like the bass from a car stereo. Al Maghnieh, a city councilor, said he helped start an investigation that established that the noise was most likely caused by a nearby steel mill.
While there is a forging plant not far from Clintonville, city officials said the work being done there does not seem to correspond with the times these noises occur.
And while the intensity of theevents appears to be decreasing in Clintonville — only a handful of people reported hearing it Wednesday night — the apprehension of some residents seems only to keep growing.
“I think somebody is drilling holes and planting dynamite,” said Gary Nielson, 60.
Other hypotheses include methamphetamine labs, sinkholes, underground rivers and even a corporate conspiracy to drive housing prices down.
On Wednesday night, to help ease anxiety, the city held a public meeting in its high school auditorium, where about 400 residents turned out.
Standing at the lectern, Kuss, the city administrator, said her best guess was that the unusually warm winter and early spring weather might have something to do with the phenomenon.
“It is possible,” she said, “that we will never have a definitive answer.”
Front Section, Pages 2 on 03/24/2012