Last night residents and National Weather Service noticed the ground shaking. 

The National Weather Service at first reported it may have been a frost quake. However, later noted that there was military exercises going on in the area. 

A 115th Fighter Wing F-16 Fighting Falcon unintentionally exceeded the speed of sound during routine night training in the airspace above south central and south eastern Wisconsin Jan. 12, at approximately 8:29 PM, according to the 115th Fighter Wing Public Affairs Office. 

The jet's speed, which caused the air to compress, resulted in a sonic boom heard by numerous Wisconsin residents.

"The 115 FW pilots make every effort to minimize the impact of their training missions to local residents," said Capt Boustany.