According to 14 News, the Vanderburgh Sheriff said that it happened near Green River and Lynch on Monday, and that they had received several calls about the strange boom sound. The sheriff said that crews had investigated but it is still unknown what caused the loud sound.
Resident Stacy Lowery said that "The sound was like a war bomb." Lowery said she had just put her children to bed and was relaxing on the couch when she heard the sound.
"A huge explosion, like definitely knew it wasn't a firecracker going off. I've never heard anything like it, very disturbing," Lowery said.
Apparently she was not the only one to hear it and the Evansville Dispatch also received several calls on Monday night between 9.30 and 11.00.
Sheriff Eric Williams told 14 News, "We obviously dispatched cars. I believe the EFD dispatched crews, the EPD. At the end of the day, we're not able to find anything."
"It had to be something a little bit different than the typical explosion," he added.
Some people thought it might be an earthquake, but USGS had no reports of any activity in the area. 14News interviewed USI Professor of Geology, Paul Doss who has been watching the seismometer just lately.
"Earthquake energy is an acoustic energy, but it would not be transmitted out of the crust and into the atmosphere. When I look over the last few days, at these times, nothing, nothing," Doss said.
Others thought it might be from a nearby mine, but Vigo, who are opening a mine in the area, said that their permit does not allow blasting between dusk and dawn.
Officials checked with the Air Force, but Lt. Mark Weaver of the Air Guard in Ft. Wayne said, "We didn't have any training events. The State of Indiana and the Air Guard, they have A10s based out of Ft. Wayne and they're not capable of executing that type of activity."
Yet others thought that maybe a meteorite had come in to land. However, Professor Jeff Braun told 14 News in the video above that there is a lack of visible evidence to prove this theory.
"Meteors can cause sonic booms when they come in, but almost always they're accompanied by a visible fireball," he said.
Sheriff Williams said, "We're going to write it off as the unexplained at this point until somebody gives us an explanation."
And so unexplained sounds continue all over the country, and no one knows why.
"At this point, nobody seems to know. The geologists say it's not in the ground, the Air Force says it's not in the air, the astronomers say it's not from space, so we're running out of options," Braun said.
Apparently strange sounds were also heard in Northern Indiana during September 2012: