CLINTONVILLE, Wis. — It was a quiet night last Sunday when the sounds began, and some residents have barely slept since.

Police here have received hundreds of calls this week from citizens awakened by noises that they said seem to be coming from under the earth. At times, they said, it was like someone banging on the pipes in the basement, while at other times it was so loud that windows rattled and the ground jolted.

City officials in this small town about an hour west of Green Bay believe there is no physical threat to residents and note that no major damage has occurred to property. But night after night of the same quakelike eruptions has inspired a local obsession — driven by fear and fascination — to pinpoint the cause.

But almost a week since it started, there is still no complete explanation for why Clintonville, population about 4,600, is booming.