As to what it's a symptom of.... I recommend that you see a physiotherapist who lifts him/herself, and they will put you through neer's test, empty can test, hawkin's test at least.
You can look up Kendall's 'testing and function with posture and pain' for more insight.
BUT in the meantime, please do not do dislocates if you feel a semi-painful grinding/popping. That is most likely going to hurt you in the long term.
Best thing you can do at present IME is to ice (new injury) or heat (older injury) the painful area, and practice good 'military posture' (the cue I give to my girlfriend re: this is 'big tits' if that helps you understand it) shoulders down and back, pinching the shoulderblades together, at all times.
I really respect the DC guys, for a lot of reasons, but I and many others have had bad experiences regarding dislocates. PM me if you need more ideas man.