Mysterious underground booms have resonated again in the eastern Wisconsin city of Clintonville.
Police dispatcher Tabitha Schoen says it was a quiet night in Clintonville until shortly after 5 a.m. when about 20 calls came in from residents who felt and heard the booms.
The booms, which have been compared to rumbles of thunder, sonic booms or fireworks, rattled homes and awakened some residents Sunday and Monday nights.
Authorities are at a loss to explain.
Seismologists have recorded unusual ground shaking in the area, similar to that caused by quarrying, mining and heavy truck traffic. But the city has ruled out such activities as possible sources of the disturbance.
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