What could be causing upper back popping?

I have a lot of “popping” going on in my upper back, especially when I sleep, turn over, and when I first get up. What could be causing this?

Is It Bad to Crack your Back? Side Effects and Risk Factors

The Truth About Back Cracking and Grinding

Shoulder Clicking, Popping, Cracking & Grinding: Causes & Treatment

4 Ways to Crack Your Upper Back - wikiHow

Hip pain: What causes it? What can you do about it?

Referred pain - Wikipedia

Why Does My Back Crack So Much?

Dislocated Shoulder: Causes, Treatment & Prevention

How to Crack Your Back: 10 Ways to Try, Video, and Tips

How to Fix Snapping Scapula Syndrome - Posture Direct

Back pain and fever: Should I be worried?

Back Acne (“Bacne”): Symptoms, Causes & Treatment

Muscle Strain of the Upper Back (Trapezius Strain)