Chances are good that the two problems are related. It is possible that the jerk on your arm injured the long thoracic nerve. This nerve activates the serratus anterior muscle, which helps hold the shoulder blade snuggly against the chest wall. When this muscle isn't working right, the shoulder blade can tilt like you've mentioned. Also, the muscle may have started to atrophy (shrink) from the nerve injury.

Both of these problems can cause the shoulder blade to pop and grate with movement of the shoulder blade. You may need to work with a physical or occupational therapist to help get the shoulder blade into better alignment. Bulking up the muscles under the shoulder blade may add just enough padding and space between the shoulder blade and chest wall to make the popping and snapping go away.