What happened to the knocking on the window that Yang Liwei heard in space?

At 9:00 on October 15, 2003, Chinese astronaut Yang Liwei carried Shenzhou 5 into outer space and went through 21 hours of space travel. At 5:35 on October 16, 2003, the Beijing Aerospace Command and Control Center sent a return command to the flying Shenzhou 5, and Yang Liwei landed safely. Later, he recalled that he was ready to sacrifice when he returned. At that time, our country's manned space technology was still somewhat immature. I remember that when Yang Liwei landed and exited the hatch, there was blood on the corner of his mouth. This was because the friction on the landing was too great, causing the microphone on Yang Liwei's neck to cut his lip. Moreover, Yang Liwei brought a Type 64 pistol before entering the space capsule, mainly because he was afraid that he would deviate from the original location and fall into danger when he returned to land, and this pistol was used for self-defense. Although Yang Liwei landed safely, in an interview afterwards, Yang Liwei also said that during the ascent of Shenzhou 5, he heard a strange knocking sound outside the space capsule door, and it was very clear. At that time, he thought it was the sound of a malfunctioning machine in the space capsule, but after listening carefully, the sound came from the outer window of the cabin door, and he also heard many errors during the return trip. This statement scared a lot of people out. A cold sweat broke out, and everyone speculated that it was a prank by aliens. Chinese scientific researchers immediately launched an investigation into this. They conducted many experiments and simulations to let Yang Liwei identify the sound, but the answers were all denied. Later, the answer was obtained by studying the aerospace industry of the former Soviet Union, because astronauts of the former Soviet Union also heard similar knocking sounds in space. After research, it was discovered that these sounds were actually the sounds made by the space capsule itself. Because during the flight of the space capsule, our space capsule will friction and heat with the atmosphere, which will lead to a similar knocking sound. After the heat generated by the friction between the space capsule and the atmosphere disappeared, the sound naturally disappeared, so the rumor was self-defeating.