PORTLAND — Chad Walls was at The Thirsty Pig one day when the horror movie “Poltergeist” was playing on the television in the corner, and he asked owner Allison Stevens if the Old Port bar was haunted.

She had no shortage of stories to tell — about the noises they hear, the balls that roll along the floor out of nowhere, the man with a pencil mustache who appears in the bathroom in the basement.

Stevens and her husband, Dave Nowers, tried spending the night there once but, between all the voices and footsteps, they couldn’t fall asleep and left before dawn. It gave Walls an idea.

He and another local musician, Joe Sweeney, run a biweekly showcase of emerging talent at the bar, called Hair of the Pig, and have been promoting upcoming shows by making silly videos that they post on Facebook. (A recent series documented the search for a missing Sweeney, with running gags about his love of Funyuns and his IBS symptoms.)

With a Halloween-themed show coming up, Walls and Sweeney wanted to make a spooky video. They thought they could sleep at the bar and film whatever happened.

“We’ve decided we need to investigate ourselves,” Walls said in an email.

To see how it should be done, they brought in ghost hunters from a Hollis outfit called Spirits Left Behind who had been to the bar before, after employees told Stevens that they were too scared to go downstairs when they had to close.

They took recordings that picked up what sounded like people talking, one as if a woman was whispering right into the microphone. Using an electromagnetic field (or EMF) meter, they asked questions and watched for it to light up in response to any activity nearby. At first, it didn’t react. That changed when they started talking about Walls and Sweeney coming back to spend the night.

Walls, who is a fan of ghost-hunting shows, had gone into the endeavor thinking it would be lighthearted, but the paranormal investigators’ findings started to change how he felt about the sleepover.

“It kind of became more serious,” he said.

Sweeney, meanwhile, is more skeptical, the Dana Scully of the duo, he said. But the footage they got that day added to the potential he saw in their film project.

“We’re basically making a mini documentary,” he said. They hope to screen it at the Halloween show, happening from 2-5 p.m. Oct. 26.

On the night of the sleepover, a Saturday in September, they waited until the last employee left around 1 a.m., then started their own sweep, asking questions, taking recordings and watching the EMF meter for reactions.

They went down to the basement, with its tight, twisting hallways and the bar’s sausage-making room, where workers often think they see someone peering out from a door behind them. That leads to the tool room, where the EMF meter starting lighting up again when they asked if their presence was welcome.

They didn’t see any shadowy figures or hear any voices, but Sweeney said he got that “feeling behind your ears when someone’s watching you.”

Upstairs, in a space used for events and as a green room for bands playing at the bar, is where their recordings picked up the most voices, what sounded like children, including one who let out a “meow” after Sweeney asked if anyone there had ever had a pet cat.

“It felt like they were kind of wanting us to be there, to hang out,” Walls said. “We got the sense that these were playful children.”

Stevens said that jibes with the feeling she has about the balls that randomly appear in the bar, including one that followed her down the stairs the day after the sleepover.

“I think that indicates someone wants to play,” she said. The Exchange Street building, which Stevens said has always been commercial, was once home to a printing press for children’s books, but she doesn’t know of any other relevant history, aside from two fires.

The number of toys in the green room, including stuffed animals and board games, is why Walls thinks it would be attractive to kids.

Nowers said he used to offer that room to bands from out of town as a place to sleep, but they would always end up getting creeped out by the noises they heard.

“No one wants to stay up here,” he said, while leading a group back up to the space to retrace Walls’ and Sweeney’s steps a couple weeks later.

As they went to leave, Sweeney turned the deadbolt to open the door, which was strange. No one who had come upstairs with them had locked it.