'Frost quakes' may be cause of mysterious noises in Muskego
MILWAUKEE (AP) — Meteorologists believe that mysterious sounds reported southeastern Wisconsin may have been caused by a rare natural phenomenon known as "frost quakes."
They happen when moisture in the ground suddenly freezes and expands.
Muskego police on Sunday received reports of loud booming noises in the city but were unable to determine the source of the sounds.
Police said there weren't any reports of damage.
Police said the noises also were heard in Waukesha, Big Bend, Wind Lake and Vernon.
National Weather Service Meteorologist Chris Stumpf said that frost quakes are a reasonable explanation for the sounds.