I have a clicking/grinding in my left shoulder. movement is fine but its sometimes sore and aches. what could this be?

Arthritis or torn ca: It could be arthritis, or a torn cartillage. I would need to know your age and more about the symptoms.

Rotator Cuff Problem: Without a proper examination, a diagnosis cannot be made. But based on symptoms it sound as if you may have a rotator cuff problem. It may be just some tendinosis or you may have an impingement and/or a partial cuff tear. Because of your symptoms you need to be evaluated by sports medicine physician or orthopaedic surgeon.

Could be joint prob.: In addition to concern about the rotator cuff, your doctor will also need to evaluate you for any intra-articular pathology like a label tear or a "slap" lesion. After a history and physical exam, often a mr arthrogram is necessary to see the shoulder anatomy. In addition, plain x-rays will also show if there is any arthritis in the joint.