Well, from what I understand the sounds CAN be just the release of say maybe gases or build up of energy then a quick release, but if you are having pain while moving, that can be more than just the old creaks and sounds joints make on occasion.
How, or did you hurt the shoulder(s)?
With your arms outstretched, does it want to splint when you rotate the arm?
Good book on the topic if you can get hold of it...
The Seven Minute Rotator Cuff Solution by Horrigan