Mysterious Underground Booms in Wisconsin

For the past few nights, residents of the eastern Wisconsin city of Clintonville have been woken up by mysterious underground booms.

City administrator Lisa Kuss said the booms have roused people from their beds and into the streets — some in pajamas. [...]

Possible explanations for the underground ruckus have been nearly exhausted, she said.

City officials have checked and rechecked methane levels at the local landfill, monitored water, sewer and gas lines, contacted the military about any exercises in the area, reviewed mining explosive permits and inspected the Pigeon River dam next to city hall.

"To me, it just seems like the most logical explanation is some earth-moving, geological thing," Kuss said. "But then why is it not happening elsewhere? It's hard to believe my little city is geographically different than the rest of the world."

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So, armchair sleuths, what could it possibly be? My money's on the Mongolian Death Worm.