To eleminate clicking/popping sound: switch off NFC.
I have also experienced that annoying clicking noise, until today when I accidentaly enter into factorytest by tapping build number, and go through all of the tests. And there was an NFC test, but I had no nfc device to connect, so I switched it off. And then the clicking sound dissappeared. I tried again to switch on NFC and the clicking sound came back, and with switching off, it disappeared. 🙂