Interestingly enough, I had a very similar issue with my Sony WH-1000XM3. They would click and pop whenever I moved my head, touched them, or simply when a door or window would open or close and produce a small change in air pressure. They would click several times in a row, every time with less intensity, before stopping. Extremely annoying. Just like with the Airpods, it would only happen with ANC on. After a failed attempt to repair them in warranty, I just insisted on getting a new pair or my money back.
I am fairly confident that in both cases it was a hardware failure.