I’ve also had this sound on my 3s, but only when handling them before putting them in my ears. I’d say it’s happened at least 10-15 times, and every time I’ve thought it’s so loud it’d do damage if it was in my ears.

Anecdotally I’ve done four 11+ hour flights with them so far and they’ve been super solid on the plane - no issues there.

Edit: here’s what I mean - https://youtube.com/shorts/VvEjetlYwa8