My iPad Air 2 that I bought 2 weeks ago was put together in the 52nd week. It didn't start to pop until after one week of use. I'd say it only pops one time a day. My theory is that it only pops above 95% battery strength. Once I'm done charging to 100% is when it happens.... I've never heard it pop lower than 95%. It will pop while in iTunes or Music or whatever. It seems to pop when the speakers switch on .... so I believe it is a battery discharge problem, to much of a surge / voltage . Too much power getting to the speakers because the battery is at full.
I dont know a whole lot about electronics, but this is what seems to be happening on my iPad. Maybe some electronic whiz can explain it. I wonder if this can be fixed through the software.... I'm not holding my breath. I can live with it, I would rather have this one then a refurbished one.
P.s. Edit. It still popped after the update yesterday.