The booming in Clintonville that has some residents losing sleep "sounds like distant thunder, fireworks or someone slamming a heavy door," the Associated Press writes.
Gather.com reports the sounds have spread 80 miles south to the town of Montello.
Residents packed a local high school to demand answers from officials. TMJ4 out of Milwaukee spoke with some of those residents:
The sounds seem to strike at night or in the wee hours of the morning, leading some people to speculate that human activity is to blame.
A scientist tells the AP he's heard from people who worry a sinkhole could open up and swallow their homes. But geologist Steve Dutch says the ground is solid and there are no fault lines nearby. Dutch speculates that low water levels could be causing the granite rock to settle.