Hearing a cracking or popping in the shoulder can be unsettling. However, unless it accompanies pain, swelling, or other symptoms, joint cracking and popping are generally harmless.
Shoulder impingement, which people sometimes call swimmer's shoulder, is a condition that causes pain in the shoulder due to a tendon or bursa rubbing against the shoulder blade.
Knee joints are under a lot of physical stress each day. It is very common to experience pain in one or both knees due to normal wear and tear, physical activity, or injury. Often, if a person has a knee injury or strain, the pain can feel as though it is burning.