Depends. It really depends on the degree, occasionally popping sounds from any joint is benign. If the shoulders are constantly producing grinding sounds or if you feel a type of clunking sensation in the shoulders, there could be a problem and you should get it checked out.
Could be other thing. The shoulder has many structures: joints, bursas, tendons. Any of these can crack. Does it hurt when it cracks? Do structures slip with the cracking? Can you feel anything? What motions of the shoulder crack. Bursitis and tendonitis are the common problems in the shoulders not arthritis. There are two joints in the shoulder: the glenohumeral joint and the acromial-clavicular joint.
Not necessarily. No, not necessarily. If you are concerned you could be seen and evaluated.