What is the reason why the turning joint will ring when sleeping?

1. This is a normal physiological reaction of human body.

This is due to the interaction of forces. In other words, when you push hard, it will affect your bones. Although there is a buffer film between bones, different forces will have different effects on the impact between bones, so sometimes it will make a loud noise.

Reference: .yahoo.com/question/1307051502621.html.