I had a lot of popping in my clutch and took it in. The first thing they checked for 'without my asking' was to see if the firewall welds were busted.
They weren't, but what they did find was that the grease for the 'action spring?' and clutch switch was completely gone. They disconnected it, used some dry packing grease or something like that. They drove my 2012 STI and 2 other new STIs on the lot and all of them had a little pop when pushing the clutch pedal down.
I will say this though, whatever they greased made a HUGE difference! My clutch is super smooth and actually noticeably easier to push in. I have my normal service in about 900 miles and am going to ask them to check it again.