CLINTONVILLE, Wis. (AP) - Sleepless families in a small Wisconsin town longed for quiet Wednesday after mysterious booming noises over the past few nights roused them from bed and sent residents into the street - sometimes still in pajamas.
The strange disturbance sounds like distant thunder, fireworks or someone slamming a heavy door. At first, many people were amused or merely curious. But after three restless nights, aggravation 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 or damage, 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.
A public meeting was scheduled later in the day to update residents on the situation.
Debby Ernst, a gas station cashier, 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," she 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 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 low-density 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 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.