My iPhone 6 screen would 'click' when pressing on certain areas as if it was not secure or something internally was broken. Also, my 'silent mode' switch on the side was not working properly and was VERY touchy. I could blow on it and it would almost switch back and forth.
Made a genius appointment and they told me that if it was just the screen issue, they would replace my screen, but since my switch was having issues as well, they just replaced it out with a new one. They didn't test/check these things I described, they just did it, no questions asked.
The replacement phone had a malfunctioning antenna/SIM port issue. It wasn't more that getting home before I turned right around to go back to Apple. My phone would switch back and forth from service to 'No Service' to 'Searching...' I first did a pit stop in AT&T to have them do a SIM card replacement but that didn't fix the issue- they advised it must be a faulty device. As soon as I walked into Apple, they welcomed me back, apologized and wasn't in there more than 5 minutes with another brand new replacement. This one is perfect, just had a run of bad luck with those two devices.
Lesson learned: pay for AppleCare, it's well worth it- and Apple's customer service is fantastic.