MILWAUKEE (AP) - A series of mysterious underground booms have been rattling a small eastern Wisconsin city for at least two nights, baffling residents and local officials who were left stumped Tuesday after ruling out numerous theories, from earthquakes to water pressure problems.
The noises - described as rumbles of thunder, sonic booms or fireworks - were being reported in northeast Clintonville, about 140 miles northwest of Milwaukee, on Sunday night but quieted down at daybreak. The sounds started back up Monday night across a wider area and continued until about 5 a.m. Tuesday, said City Administrator Lisa Kuss.
"There's no warning, it's just "bam,'" Kuss said. "I would describe it as startling, an adrenalin rush. ... Your heart is instantaneously kind of racing because you are not expecting it."
Local resident Al Miller said he's been hearing rumblings for a couple weeks but chalked it up to thunder or didn't think much of it. But an especially loud boom woke him around 3 a.m. Monday.
"My house shook and it was just like a shock," the 71-year-old said. "I got out of bed and was like "Wow.' I thought one of my trees fell onto the house."
When he went outside and saw the trees still standing, he also noticed his neighbors' lights popping on because they'd heard it, too.
Harold Tobin, a University of Wisconsin-Madison seismologist, said there are similar reports of booms in different parts of the U.S. and world from time to time. Sometimes they're explained, sometimes they're not, he said.
"I'm as intrigued and as puzzled as other people are," he said Tuesday.
A seismic station near Clintonville has recorded unusual ground shaking since Sunday night. Tobin said such activity can be caused by quarrying, mining and heavy truck traffic, but since the city ruled out those sources - there are no mines or major construction in the area - the university and the Wisconsin Geological and Natural History Survey will likely take a closer look at the station's data.
Kuss speculated that something within Clintonville may be causing the noises, since no one from outside the city of 4,500 residents has reported hearing them. No one has been hurt, and no damage has been found.
Authorities trying to track down the source found no gas in the sewers or problems with the city water pressure or wells, and nothing was found at an area landfill that might explain the rumbling, Kuss said. Engineers also checked a nearby dam and ruled it out, and there are no nearby industrial businesses or military operations making the noise, she said.
There also have been no recorded earthquakes in the area.
Some residents were just as frustrated as city leaders, and a bit sleep-deprived after being woken up for two straight nights.
"When it first started happening it was kind of scary," said 21-year-old Jordan Pfeiler. "Then it was cool in a way. Now it's just annoying. I want it to go away."