Nothing's been booming or shaking in Clintonville for a few weeks so siesmometers and sound sensors were being pulled out of the ground and packed up Monday.

A swarm of minor earthquakes that besieged the city in late March -- rattling windows and disrupting sleep -- grabbed international headlines and spawned rumors about what could be causing the unusual vibrations and accompanying loud noises. But no aliens, underground mines or secret tunnels were found.

Scientists at the Wisconsin Geological and Natural History Survey in Madison said the low-intensity seismic activity likely was produced by a phenomenon known as post-glacial rebounding.