HAve you run a bench mark test? There are a couple really good apps that run benchmark tests. Geekbench 3 and Preformance Test. With geekbench if everything is running correctly your multi core score should be 4511-4530 or higher & single core should be around 1812-1820 or higher. These tests focus on graphics, processor, screen, battery and RAM. the five most important elements of an iPad. When my first iPad Air 2 started popping out if the box I ran those tests and I was getting half that. On the other two that popped the scores were higher but either way your device should not be making an arcing pop noise. If it is take it back for an exchange or refund. I went through four and so far this iPad has been working just fine. I use it for work and play so i am on it nonstop. When I returned the last iPad Air 2 the tech did confirm it was hardware. The sound that most people are hearing and feeling comes from the upper left hand side of the back in book format. If you think it is the speakers then there maybe a totally diferent issue and there are posts for that.
THey have sold over five million iPads and this popping issue is really a very small percentage of properly running iPads. with that being said, that alone spells hardware. In addition there have been four major updates since coming off the line and one did address an issue with EQ but that was unrelated to this.
THere is no common pattern some that do it are week 1 - 44. In this situation it really sounds as if a few employees just did not do their job and some bad iPads were sent out and sold it happens with everything and Apple, of course, is not immune.
I Have friends that bought when they first came out and theirs run just fine. I have several employees the same and then i know two other folks that just bought theirs and theirs popped and they returned them right away and got ones that work just fine. I was going to wait until after the new year but a client gave me one for Christmas and it works well no popping or screen issues. I have run stress tests, battery tests, graphic tests, processor tests, and all passed. in addition you can call Apple Customer Care and ask to send you a diagnostic link to run on your iPad and they can check your motherboard, processor, battery, RAM, etc... In a few minutes.
I Really hope you can return your iPad Air 2's for an exchange or a refund and wait until you feel more comfortable about buying one again. I had troubles but after receiving one for Christmas i got a good one as the millions of others. So dont give up keep returning them until you are satisfied or get a refund. I was told if you bought one after november 1st there is a holiday return policy of the 1st of November until the 8th of January. At least in my neck of the woods it is that way. I wish everyone al, the best and happy new year.