Mysterious “Booms” in Wisconsin

As I was perusing the news this morning, I noticed an intriguing article about Mysterious Booms in a Wisconsin town. I pulled up the article thinking that it would be simply a funny story about someone doing something stupid. The booms have been occurring since Monday evening and the city has tried to determine the source to no avail. Read more details about the story from the Associated Press. The article and other articles I have found are written by journalists so they are short and don’t include a lot of details.  This has left questions for me, particularly, are the booms only occurring at night, or do they occur during the day as well? If they are only occurring at night, I would suspect that that may help narrow down the source.

I did a little more research and came across a blog: Mystery Booms / Skyquakes.  The author details a number of occurrences of incidents that sound similar and attribute the cause to small disturbances beneath the surface, much like an earthquake only substantially smaller to where only those right next to it would feel it. This could be the case, however, the cities preliminary investigations note that the city doesn’t sit on or near a fault line and that the bedrock is composed of mostly granite. The city hired a seismologist and an engineering team to do a more detailed look and get to the bottom of the situation, so hopefully they’ll have an answer soon.  What thoughts do you have? Any seismologists or geologists that could shed light on this? Any theories?