I have the popping EVERYWHERE! Knees, ankles, wrists, back, neck, shoulders, wrists fingers, toes, even my jaw. If its a joint on me it pops and crackles. Im ALWAYS saying just call me rice krispies, lol. Its NOT damaging or dangerous so please dont worry that its something horrible. Its just gas escaping between the joints during movements. Tends to happen when we move after getting stiff. It is seriously nothing to panic over. Your doctir has even said the same thing, though likely with a LOT less explanation.