An astronaut aboard the International Space Station reports that the empty Boeing Starliner capsule docked at the station has begun making strange noises, the cause of which has baffled NASA engineers on the ground and amateur space sleuths. Captain Butch Wilmore, who has been aboard the space station for nearly three months, radioed back to Earth on Saturday to ask them to help decipher the noise. 

“There’s a strange noise coming through the speaker, and I didn’t know if you could connect into the Starliner and hear,” Captain Wilmore said. He then held his microphone near a Starliner speaker inside the craft, which emitted a distinct pulsing sound that resembled cymbals. The man at Houston who was receiving Captain Wilmore’s transmission described it as a kind of “solar 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,” Captain Wilmore said. After holding the microphone up to the speaker again, engineers at Houston’s Mission Control told the astronaut to “call us if you figure it out.”

The audio of Captain Wilmore’s call to Houston was captured by a Michigan meteorologist named Rob Dale, who shared the clip on a website forum for discussions about space. A number of users commented on Mr. Dale’s post on Saturday, writing that “Someone’s knocking at the door!” or that the British show “Doctor Who” was actually real. One user lamented the fact that the International Space Station’s communications live feed on YouTube was down, and that curious observers could not get more information. 

The Starliner, which was manufactured by Boeing, is set to leave the space station on September 6, and has faced a number of technical issues since launch just a few weeks ago. Captain Wilmore and his fellow astronaut, Captain Sunita Williams, were due to come home from the space station on the Starliner after just eight days in orbit, though a number of technical problems kept pushing the return date further and further back.

Eventually, NASA made the determination that Captain Wilmore and Captain Williams would stay aboard the space station until early 2025, with a different aerospace company, SpaceX, bringing them home at that time. 

The Boeing Starliner suffered from Helium leaks and problems with a majority of its thrusters earlier this year. The Starliner trip was originally planned for 2017, though setbacks — including oxygen leaks, malfunctions with parachute harnesses, and the accidental use of flammable tape — caused the launches to be delayed significantly. The first two uncrewed flights were deemed partial failures. 

NASA’s administrator, Bill Nelson, announced on August 24 that while Boeing’s Starliner program will not end, it will be Elon Musk’s SpaceX that brings Captain Wilmore and Captain Williams home next year. Boeing “expressed to me an intention that they will continue to work the problems once Starliner is back safely,” Mr. Nelson told reporters after the decision was announced.