Yang Liwei, 51, has told in an interview how he heard the inexplicable bang – described as being like a “wooden hammer hitting an iron bucket”, during his maiden space flight in 2003.
Liwei, who is China’s first astronaut, admitted being baffled by the noise which he said appeared “suddenly without any reason”, on more than one occasion, according to Xinhua news agency.
Yang said: “A non-causal situation I have met in space is a knock that appeared from time to time.
“It neither came from outside nor inside the spaceship, but sounded like someone is knocking the body of the spaceship just as knocking an iron bucket with a wooden hammer.”
Yang, now a major general, said he was went outside to investigate the ship, but remained perplexed when he could not find anything that would have been responsible for the noise.
Yang is not alone in hearing the noise, which has also been reported by spaceflight mission Shenzhou 6 and Shenzhou 7 astronauts.
But the men on the mission were also unable to explain the source.
Yang said: “Before entering space, I have told them that the sound is a normal phenomenon, so there is no need to worry.”
Yang tried to find an explanation while back on earth by discussing the noise with technical experts.
So far, nobody has come up with a satisfactory explanation, nor been able to recreate the noise using objects or instruments.