Hold it and while on a fairly decent volume level, play a game or do anything touching the screen. The back vibration is the worst amongst any Ipads and none of them gave any vibration/feedback to the front screen at all when doing things.
It's annoying, not a deal breaker and very tolerable because I use earbuds and external speaker as well mostly. I can see why folks that don't really don't want to live with that, why does that amaze you??? As far as a defect? Android tablets thin and light do not experience this, I have experience with many with the most recent the 4th gen Kindle Fire HDX 8.9" which probably has the best sound on the planet.
The vibration in itself however would never keep me from the Air 2. The $100 savings, probably would get an Ipad Air 1 still on IOS 7 (the consensus is IOS 8 is buggy), absolutely better battery life and I doubt I'll notice much of a speed difference to tell the truth. More fuel why some folks would revert back to the Air 1.
Thanks for your feedback. I'm not going to the Air 1 just yet, just kicking it around. There are just as many folks happy with the move to the Air 2 from the Air 1 as the reverse.