Moto G bottom right corner case clicking/creaking mildly

[RJDG14]

So I've had a Moto G for about 8 months now and have generally been satisfied, although this morning I found that the corner of the phone (bottom right) was creaking when I pressed on it and pushed my thumbnail into the crack to try and resolve the issue. So I tried replacing the case with an unused spare one that I had, and the problem is still occuring (not quite as much, though). How do I reduce or stop the issue? I'm just having quite a stressful time right now as a result of what has been happening. The clicking issues began a few weeks ago when I discovered that the "strange white bit" in the gap on the left was that the SIM card end hadn't been properly removed, so I took the case off for the first time in 8 months to resolve the issue. But then a few days later, I began having more clicking issues with other various corners. This has resulted in me removing the case several times to try and resolve the issue. The phone still works fine, although the issue is just very annoying! Please try and help me resolve the issue. Is there a way to stop the problem? Why has it only started occuring since I removed the back?

 

[RJDG14]

It's later in the day and there are still some minor issues, yet they aren't as bad as earlier. For some reason the phone case seems stronger after a few minutes outside (at roughly 25° in the UK).