Geophysicists said late Thursday the source likely can be traced back to an earthquake that measured 1.5 Tuesday evening.
Clintonville City Administrator Lisa Kuss said the city will shell out the sum to engineering firm Ruekert & Mielke to have four seismometers attempt to pinpoint the epicenter of the booming, which Kuss said is believed to be a couple hundred feet under the surface, The (Appleton) Post-Crescent reported Thursday.
"It's possible we'll never have a definitive answer," Kuss said at a public hearing Wednesday.
Officials said calls have come in from all over the city about mysterious booming sounds and vibrations, which began Sunday night. Kuss said the phenomenon seems to be waning, with fewer booms reported each night.
The U.S. Geological Survey said the quake struck at 5:15 p.m. Tuesday 30 miles northwest of Appleton, 37 miles west-northwest of Green Bay and 40 miles east of Stevens Point about 3.1 miles below the earth's surface. The continuing booms could be so-called microquakes that can be felt only nearby, Gannett newspapers reported.