s6 possible back plate defect?

I was wondering if anyone else can confirm this issue. I was removing fingerprints from the back of my s6 with my shirt and I realized that when i push or rub the middle of the back of the device in a certain way, it pops or makes a click noise. I don't see anything moving, it just sort of clicks lightly. It is most apparent when you hold the phone horizontally from the top and bottom and push or rub the middle of it. I can replicate the click and motion that causes it every time. Is this normal or possible a loose backplate? Thanks!