You may or may not hear a popping noise, similar to the noise you hear when you "pop your knuckles". This noise is a side effect of the adjustment and is painless and not harmful. It is nitrogen gas that enters the partial vacuum created when the joints are slightly separated.You may or may not hear a popping noise, similar to the noise you hear when you "pop your knuckles". This noise is a side effect of the adjustment and is painless and not harmful. It is nitrogen gas that enters the partial vacuum created when the joints are slightly separated.