you might want to consult a medical professional

Many of the body's joints often make crackling sounds with movement under normal conditions, including those in the spine. Painless crackling is usually caused by gas bubbles forming in the fluid surrounding the joint as the joint capsule is stretched, which is usually harmless (although some studies show a risk of soft-tissue damage associated with frequent knuckle-cracking). Tendons and ligaments can also make crackling sounds as they snap back into position after stretching. Degenerative conditions which can cause crackling, such as arthritis or compression fractures, are usually painful.

If you've just recently increased your exercise regimen at age 71, a consultation with a doctor is a good idea for cardiovascular reasons alone, and you could mention your crackling back as well. If you're otherwise healthy, painless crackling is nothing to worry about, but see your doctor if the crackling becomes associated with pain, stiffness, or especially numbness or weakness.

Diet and workout maintain bone health. Do you have a special diet? I have read on Project Weight Loss how to achieve a balance between losing weight and preserving the bone. Calorie restriction should not be considered a negative, as it helps reduce the risk of disease and contributes to losing weight.It is also possible that calorie restrictions may result in anti-aging benefits, which could not be achieved solely by exercising.