Why do our bones crack inside of our bodies?

it sounds crazy. its like hitting metal with a piece if nail. thats what it sounds like.Why do our bones crack inside of our bodies?
because your weak and your joints are rusty. Similar to a door that hasn't been used in a while, the hinges tend to creak. The human body is the same way if you don't exercise your bones become rusty like those hinges on the doorWhy do our bones crack inside of our bodies?
Your body is a machine, and machines make noises