How long did it take for the 2nd phone to start clicking?
Watching the YouTube movie and how easily the girl can remove the issue it appears that it takes just a bit of stress on the shell to set it off--no need to truly bend it.
I will wait for my visit at the Apple Store and see what they recommend ....
UPDATE: I went to the Apple Store and they did exchange the phone, no questions asked. The employee said it was due to a manufacturing defect, the glass did not bond properly to the LCD. I asked if it has been a common issue and he said not very common for iPhone 6, he said he saw 2-3 iphone 6 with the same issue.
Anyway, new phone for me, the process was easy, I had a iCloud backup, so smooth sailing and walked out of there with a new phone in half an hour. I will post again if I will have problems with the new phone, so far so good. FYI, I have now the phone in a case.