Clintonville city officials might deploy motion sensors to help determine the source of mysterious rumbling and ground vibrations that have continued to frighten and mystify residents.

For the second consecutive day, this Waupaca County community remained in the grip of unexplained booming, rattling and thunder-like noises, City Administrator Lisa Kuss said. No injuries have been reported, and there has been no damage to buildings or pavement.

Most complaints of booms, bangs and shaking houses come in the dark of night, but authorities have offered no solutions to the mystery in the light of day.

Public Works Director Mike McCord has a name for the phenomenon. "We suspect it is some type of shallow ground disturbance," he said Tuesday. That means it is not an earthquake.

The noise and the shaking seem to be coming from the southeast and moving across the northeastern corner of the city, McCord said.

A public meeting is scheduled at 6 p.m. Wednesday in the auditorium of Clintonville High School, 64 W. Green Tree Road. Kuss and other officials will share information on the disturbances.

An estimated 100 calls to police Monday evening and early Tuesday came in a clear pattern, with calls clustered at 8 and 10 p.m. Monday, midnight, and 1 and 2 a.m. Tuesday, Kuss said.

Police reported receiving about 150 similar complaints of loud, rumbling noises accompanied by windows rattling and houses shaking beginning about 2 a.m. Monday.

McCord was awakened by a noise early Monday.

"The first time it came through Clintonville, I thought it was distant thunder."

He has heard loud, unexplained noises more than a dozen times in the last 72 hours, McCord said. He has been inside the city's water utility building on E. 12th St. when the phenomenon came through.

"In a structure, it sounds like someone dropped a 50-pound weight on a concrete floor," he said. McCord described the sound as a muffled boom outdoors.

Some of Tuesday's complaints were from neighborhoods south and west of the locations of Monday's calls, which were centered in the northeast side of the city, Kuss said.

By Tuesday morning, authorities were rechecking utilities they had investigated a day earlier as possible sources of the booms.

"We checked water pumps for our well" and the city's drinking water distribution system, Kuss said. City officials checked a dam on the Pigeon River for damage and asked local industries about overnight activities.

Electrical utilities have been checked, and natural gas pipelines have been tested for leaks.

"We've taken some extreme precautions to keep our residents safe," McCord said.

Scientists are telling Kuss that this is not seismic activity. It is not related to a local dump and it is not being caused by the sewage treatment plant on the river. It is not being caused by military activities, blasting, quarrying or sand and gravel mining, Kuss said.

Kuss said she is still waiting for someone to tell her what it is.