Evansville-area resident Caleb Donahoo said he's heard the booms and the first of them, just before midnight Monday, was so loud it shook his home.
"I was asleep, and it woke me up. It rattled the windows and the house and everything," Donahoo said Wednesday evening.
Evansville-Vanderburgh County Emergency Management Agency director Sherman Greer told the Evansville Courier & Press for a Thursday story that authorities from several agencies have investigated the booms but haven't had any luck tracking down their source.
Greer said he's checked with the state's Department of Homeland Security and the Indiana Geological Survey, but those conversations produced no useful information.
A group of meteorologists at the National Weather Service's Paducah, Ky., office couldn't offer any weather-related explanations for the booms. And Vectren Corp. spokeswoman Chase Kelley said the company has no record of any blown transformers in any of the areas where the sounds were reported Monday and Tuesday night.
But she said several Vectren workers had asked a supervisor if a blown transformer was a cause of any of the sounds.
Greer said has no idea what could be causing the booms, which have stirred up plenty of speculation.
"We've been more or less listening to the chatter over the radios and what's going on Facebook and Twitter and everything else to see what other people are saying," he said.
The booms have fueled rampant speculation on social media, with theories ranging from a blown power transformer to a meth explosion or a sonic boom from some sort of aircraft. Others have speculated the noises could be mine blasts at a nearby coal mine.
But Evansville-based Vigo Coal, which operates in Boonville, said its permit prohibits blasting work from dusk to dawn.
Donahoo said he hopes the source of the booms is found soon.
"Somebody out there knows. Now it's just who is going to step up and say, 'Yeah, we know what's going on,' or 'Yeah, it's our fault,'" he said.