It was the topic of the day in North Stamford neighborhoods Friday - what was that noise that shook homes and even rattled pictures off walls?

“Everyone was like, ‘Did you hear that? How did it feel to you?’ And it felt underground,” said Louanne LaMonico Sack, who lives on Wake Robin Lane.

Around 6:30 p.m. Thursday, while in the kitchen, LaMonico Sack experienced a first.

“My son and I were standing up and we felt under our feet like this rumbling, and it sort of sounded like a bang,” LaMonico Sack recalled.

There was also the reaction from her miniature poodle, Lucky.

“This little guy went crazy, and dogs are the first to know, you know, if something is wrong. He just wouldn't stop barking, so he felt it, too. It kind of gave him like a little jolt. He just jumped up, and then he was barking,” she told News 12.

LaMonico Sack said she initially thought a big tree had fallen on their property, so she ran outside to look but didn’t see anything. She wasn’t the only person puzzled.

Stamford fire officials said a series of calls came in from neighborhoods mostly north of the Merritt Parkway, reporting a loud explosion. The first round of reports was from 6:30 p.m. to 7:20 p.m., according to officials. Then around 3:45 a.m. Friday, people called in to say they were woken by the same explosive sound and tremors.

“They were spread out over a geographic area of maybe one or two square miles in North Stamford,” Stamford Fire Chief Rex Morris explained.

But each time crews responded they found nothing.

“There's usually a signature. You know, there's a house that's been damaged or there's a fire or there's a cloud of smoke. There is something. These places were all intact,” Morris explained.

The initial thought was maybe a utility issue, especially since a major transmission line from the Tennessee Gas Pipeline runs through the area, so officials reached out.

“There's the pipeline up there, plus our Eversource gas lines run pretty much everywhere in the city. And they checked their systems and reported no damage, no leakage,” stated Morris.

Crews returned to investigate more once the sun came up but still didn’t have an answer.

“All the things we'd normally say, ‘Well maybe that was affected or that was the cause,’ they weren't,” Morris told News 12, adding that fire crews also searched for a blown transformer or car crash.

“It was not something we're used to around here. This isn't California,” LaMonico Sack said with a laugh. “No one's saying anything, so I assume it could've been an earthquake.”

Fire officials have reached out to the U.S. Geological Survey to determine whether there was any seismic activity that could explain the noise and rumblings. Morris said there weren’t any similar reports in neighboring towns, and they’ve ruled out a sonic boom.

“We're chalking this one up - for right now - as undetermined and somewhat of an anomaly that made a lot of noise. Has to be something to it because we had a lot of calls on it,” Morris stated, adding that they’ll continue to monitor the situation.

Officials understand people are concerned but said they are committed to keeping the community safe and confident there is no immediate danger.

“People can rest assured that there was no problem. But if they have any issues in the future, notify us, and we will do a thorough investigation,” said Morris.