The strange disturbance sounds like distant thunder, fireworks or someone slamming a heavy door. At first, many people were amused. But after a third restless night Tuesday into Wednesday, exasperation is mounting. And some folks are considering leaving town until investigators determine the source of the racket.
"My husband thought it was cool, but I don't think so. This is not a joke," said Jolene Van Beek, who awoke early Sunday to a loud boom that shook her house. "I don't know what it is, but I just want it to stop."
The booming in Clintonville continued Monday and Tuesday nights and into Wednesday morning, eventually prompting Van Beek to take her three sons to her father's home, 10 minutes away, so they could get some uninterrupted sleep.
There have been no reports of injury, despite some residents saying they could feel the ground roll beneath their feet.
City officials say they have investigated every possible human cause. They checked water, sewer and gas lines, contacted the military about any exercises in the area, reviewed permits for mining explosives and inspected a dam next to City Hall. They even tested methane levels at the landfill in case the gas was spontaneously exploding.
"People in the area are certainly frustrated," City Administrator Lisa Kuss said.
The city is also investigating geological causes. Officials plan to bring in vibration-detection devices to try to determine the epicenter of any underground activity.
Authorities set up audio and video equipment overnight but didn't capture any evidence of shaking or booming despite at least one loud noise about 5 a.m. Wednesday, Kuss said.
About 300 people attended a public meeting Wednesday night in a local high school auditorium to get an update on the situation. Kuss assured residents that officials are doing everything they can to determine the source of the booming.
Sharon Binger said the disturbance has left cracks in her basement walls and floor, and that they're getting worse. She said her insurance company won't pay for the damage until she knows what caused it.
"This is an issue," she said, demanding answers from officials at the meeting. "There is something else going on."
Kuss urged Binger to write down when the cracks occurred and promised to send officials to the woman's home to look over the damage.
Debby Ernst has not heard the sound or felt the tremors but said she is still considering going elsewhere until the mystery is solved.
"It worries me. I'm scared," Ernst, a gas station cashier, said in a phone interview. "Who's to say it ain't going to get worse?"
However, a local scientist said nothing has surfaced that suggests townspeople should be afraid.
Steve Dutch, a geologist at the University of Wisconsin-Green Bay, said the ground beneath them is solid, and that there are no known earthquake fault lines in the area.
Dutch said he heard some people worrying that a sinkhole might open up and swallow homes. That can happen in areas where the ground is rich with limestone and other rocks that can be dissolved by water, he said. But the rock below Clintonville is mainly solid granite that's largely impermeable.
However, he speculated that water and granite could hold the key to the mystery. Granite has small cracks that water can fill, but if the underground water table falls especially low, water can seep out, leaving gaps that cause the rocks to settle and generate loud noises.
"Maybe the very dry winter caused more water to be removed from the water table, either through pumping or natural flow," he said.
A seismic station near Clintonville, a town of about 4,600 people about 40 miles west of Green Bay, has recorded unusual ground shaking since Sunday night. Scientists say such activity can be caused by mining and heavy truck traffic, but since there are no mines or major construction in the area, the Wisconsin Geological and Natural History Survey will take a closer look at the data.
Some residents are having fun with the mystery, which has drawn media attention from around the nation.
Jordan Pfeiler said people stayed up late on the first two nights to walk around listening for booms. They came up with outlandish theories to explain the noise -- for example, that the White House was building an underground bunker in the area or that mole men had found a home there.
"And the aliens, of course, there's always the aliens," she said.
Van Beek understands the temptation to crack jokes, but it's no laughing matter to her.
"Everything people think it is has been ruled out. They just don't have answers," she said. "At this point all I want is for it to stop."