I had the sane problem develop and the left AirPod replaced in January. The replacement AirPod started showing the same symptoms.
When I had that one replaced the “Apple Genius” was rather argumentative about it. He says there are no moving parts in an AirPod and he hasn’t come across this problem ever.
Any idea where this rattling noise could stem from?
It only seems to be noticeable when either ANC or transparency mode is turned on.
HERE...
Suck on ‘em (to fix crackling issues!!!)
Sorry, I know it sounds indelicate and weird. I don’t mean, “They’re terrible products, so suck on ‘em”... I mean, quite literally, that if you’re having sound issues, then actually suck on them. If you’re experiencing popping and/or crackling noises - especially in Noise Cancelling or...forums.macrumors.com
I have found the tru cause