NASA astronaut Butch Wilmore reported a "strange noise" on the Boeing Starliner space aircraft, leaving him and colleague Suni Williams stuck in space six months longer than expected following their launch in June. 

“I’ve got a question about Starliner,” Wilmore said, radioing mission control in Houston on Saturday. “There’s a strange noise coming through the speaker … I don’t know what’s making it.”

The astronaut reported a pulsing sound from the capsule's speaker. However, this is not the first problem Wilmore and Williams have faced since blasting off, encountering helium leaks and propulsion issues.

The source of the pulsing noise on the spacecraft is believed to stem from a feedback loop between the space station and the Starliner.

“Alright Butch, that one came through,” Mission Control told Wilmore during their probe when the astronaut placed his microphone up to the speaker.

“It was kind of like a pulsing noise, almost like a sonar ping.” Wilmore radioed back, adding, “I’ll let y’all scratch your heads and see if you can figure out what’s going on … Call us if you figure it out.”

The space aircraft is set to return to Earth on September 6, landing in New Mexico through autopilot while the astronauts are expected to return in February in a capsule built by Boeing competitor SpaceX.

To accommodate Wilmore and Williams, two NASA astronauts scheduled to join the International Space Station will be excluded from a mission later this month.

The strange sound was captured and shared by Michigan-based Meteorologist Rob Dale and initially reported by Ars Technica. The report highlighted that audio difficulties on a spacecraft were not an unusual occurrence. 

Astronauts stuck in orbit to return in February, NASA says

NASA announced in late August that the two astronauts, Sunita “Suni” Williams and Barry “Butch” Wilmore, who have been stuck on the International Space Station for months, will return to Earth on a SpaceX-crewed Dragon flight in February.

This was decided after consultations and reviews with Bill Nelson, the agency administrator, all of which later determined that a return on their initial spacecraft, Boeing’s Starliner, included too many uncertainties after leaks and failed thrusters were discovered. 

Butch and Suni boarded the Boeing Starliner on June 6 before it was approved by NASA, and were scheduled for an eight-day trip which soon turned into months of waiting amid the dysfunction of the craft's thrusters as it first tried docking. 

Both astronauts have since taken part in space maintenance and have reportedly recorded over 100 hours of work across 42 different projects. 

Currently, four out of the five thrusters have regained function. The Associated Press explained that the thrusters' role was to ensure the correct positioning of the craft after it undocks. 

On August 2, Boeing announced that it had extensively tested the propulsion system of its Starliner spacecraft, confirming that 27 of 28 thrusters were fully operational. Despite these improvements, Boeing, which has faced challenges competing with SpaceX and incurred $1.6 billion in losses on the Starliner program, will bring the spacecraft back uncrewed in September.