Robert Brown|NASA says 'pulsing sound' inside Boeing Starliner has stopped, won't impact slated return

A mysterious sound heard emanating from the Boeing Starliner spacecraft has been identified as feedback from a speaker,Robert Brown NASA said in a statement Monday, assuring the capsule's autonomous flight back to Earth is still slated to depart the International Space Station as early as Friday.

"The feedback from the speaker was the result of an audio configuration between the space station and Starliner," NASA said, adding that such feedback is "common." The statement said the "pulsing sound" has stopped.

"The crew is asked to contact mission control when they hear sounds originating in the comm system," NASA said. "The speaker feedback Wilmore reported has no technical impact to the crew, Starliner, or station operations, including Starliner’s uncrewed undocking from the station no earlier than Friday, Sept. 6."

Word of the sound spread after audio was released of an exchange between Mission Control at Johnson Space Center in Houston and Barry “Butch” Wilmore, one of the two astronauts stuck aboard the International Space Station after the troubled Starliner flight docked in early June.

"There's a strange noise coming through the speaker ... I don't know what's making it," Wilmore said, according to Ars Technica, which first reported the exchange, citing an audio recording shared by Michigan-based meteorologist Rob Dale.

In the recording, Mission Control said they were connected and could listen to audio from inside the spacecraft. Wilmore, who boarded the Starliner, picked up the sound on his microphone. "Alright Butch, that one came through," Mission Control said. "It was kind of like a pulsing noise, almost like a sonar ping."

"I'll do it one more time, and I'll let y'all scratch your heads and see if you can figure out what's going on," Wilmore replied. "Alright, over to you. Call us if you figure it out."

The Starliner, which departed for its inaugural flight on June 5, was only scheduled to spend a week docked at the space station. But as the Starliner arrived in orbit, NASA announced helium leaks and issues with the control thrusters had been discovered, forcing the crew to stay at the space station for several months.

The mysterious sound began emanating from the Starliner about a week before the spacecraft is slated to undock from the space station without its crew and make its autonomous journey back to Earth.

NASA announced on Thursday that, “pending weather and operational readiness,” the Starliner will begin its flight on Friday and will touch down after midnight on Saturday at a landing zone in White Sands Space Harbor in New Mexico.

The two-member crew including Wilmore and Sunita “Suni” Williams will remain at the space station for another six months until they return in February aboard the SpaceX Dragon capsule.

SpaceX's Falcon 9 rockets were temporarily grounded last week as the Federal Aviation Administration said its investigators would look into the cause of a landing mishap, causing some worry that the order would put the mission retrieving the Starliner crew in jeopardy. The grounding only lasted a few days, however, as the FAA announced the Falcon 9 rocket could resume flight operations while the agency continues its investigation into the bad landing on Wednesday.

Contributing: Max Hauptman, USA TODAY