babies shoulders pop

Please help I'm a ftm and I don't know. I've heard my little girls shoulder pop after I've picked her up under her armpits to put her over my shoulder to burp her. It doesn't seem to bug her. Tonight it happened and she cried shortly after and would stop too. She had a dirty diaper so I know that was part of it. She cried too when she didn't want to be in her swing. She is moving the arm that popped just fine. And when I moved it around she didn't cry. Is it normal for their shoulders to slightly pop?