I have myself noticed this same problem everyone else has posted about. It's very random, one-and-done, and can't be reproduced. I probably hear it every 3-4 days but even that varies. Seems to mostly happen (that I've notced) when using the new Home Touch ID button. Mine is a 64GB WiFi model. It probably was one of the first to come out of the factory as it was available for sale at one of my local Apple stories Wednesday, two days before the "official" on sale date.
I have not noticed any other glitches and my iPad operates normally otherwise. This is my fifth iPad (never bought the original 2) and have NEVER had an issue with any of them. If the pop becomes more persistent then I might look for a replacement but I'm inclined to keep this one for now. I have the original 1-year warranty. If it goes in 3 or 6 months, my new one will have a years warranty from that date.