system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do joints make a "Cracking" noise for certain activities such as walking up stairs, but have no actual pain associated with them?
gpt
The generally accepted reason is the diffusion of (and the resulting collapse of) gaseous bubbles in the fluids between your bones/cartilage. 

The debate is still out on whether it’s the bubble forming that makes the sound or the bubble collapsing that makes the sound. 

However you’ll notice you can only crack joints that you haven’t moved in a while, which allows the gasses to diffuse. Then you can pull the joint apart creating a void which is promptly filled by the gasses diffused in the fluids surrounding the joint as the pressure drops in that area. Eventually pressure returns to normal and the bubble collapses. 

Again, generally it’s accepted that the collapse of the bubble is the cause of the sound but the debate is still out on that.