I’ve experiencing this same issue on every flight now using APP3, and considering returning. Tried multiple different ear tip sizes. Reset and re-paired. It’s not just pressure changes, as it occurs at steady altitude in addition to ascending and descending. I’m very surprised Apple didn’t catch this issue by testing the ANC on aircraft more extensively during product testing, since that is an extremely common use case for ANC headphones. They also generate weird popping/thumping noises while running, or tinny echoes sometimes while scratching my head. Hopefully there is a software fix. AP1 ANC worked just fine (until case failed to charge left earbud).