Stranded NASA astronaut reports hearing 'strange pulsing noises' in urgent call

Two NASA astronauts stranded on the International Space Station have been plagued by "strange noises" coming from the ill-fated spacecraft they arrived on.

Just days before Boeing 's Starliner is set to return to Earth on autopilot, Butch Wilmore radioed Mission Control telling Houston they had a problem.

In an audio recording of the exchange with staff on the ground at Mission Control at Johnson Space Centre, the astronaut holds up a phone to the speakers. After initially being inaudible, a pulsating sound emanating at steady intervals can be heard through Wilmore's device.

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"Butch, that one came through... It was kind of like a pulsating noise, almost like a sonar ping," Mission Control told him after not hearing it the first time.

"I'll do it one more time and let you all scratch your heads and see if you can figure out what's going on," Wilmore told Mission Control, playing the sound again. The astronaut clarified the noise emanated from the Starliner speaker. The cause of the sound is yet to be determined.

This week, Starliner is slated to undock from the ISS, empty, and attempt to return on autopilot with a touchdown in the New Mexico desert.

Starliner's test pilots Wilmore, 61, and Sunita 'Suni' Williams, 58, embarked on what was supposed to be an eight-day trip to the International Space Station on June 5.

However, when thruster and leak problems hit Boeing 's Starliner capsule after lift-off, it meant that they wouldn't return as scheduled.

On August 8, NASA 's Commercial Crew Program manager, Steve Stich, said that the pair's most likely choice could be to return home on Space X Crew-9's return flight in February.

"We have been working with SpaceX to ensure they are ready to respond with Crew-9 as a contingency. We have not formally committed to this path, but we wanted to ensure we had all that flexibility in place," Stich said.

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"Our prime option is to return Butch and Suni on Starliner. However, we have done the requisite planning to make sure we have other options open."

After years of delays and ballooning costs, Boeing had counted on Starliner's first crew trip to revive the troubled spacecraft program. The company had insisted Starliner was safe based on all the recent thruster tests in space and on the ground.