WI (Clintonville) Residents Experience Loud Booms, Ground Shaking 3/19 3/20

WI Residents Experience Loud Booms, Shaking in the Ground 3/19/12

http://www.postcrescent.com/article/20120320/APC0101/120320005/night-booms-Clintonville

Something's rattling small Wisconsin town - CNN

I haven't experienced these booms, I am too far south.  Cannot explain except for seismic activity.