So as mentioned in my previous post, I’ve now had the left earbud replaced and it’s all good.
But just to clear up what *I* perceive the issue being: it’s a physical defect, not a software one.
When the issue happened, it was when the earbuds were effectively ‘turned off’ and not being used. Whenever i moved or especially walked, there was some rattling sound in the earbud(s) that happened whoever I moved or, say walking/running, would happen when my heel connected with the floor.
Trying to adjust the earbud in my ear didn’t help; it wasn’t that ‘squishy/squidgy’ sound like moisture or stickiness. If I lightly tapped the earbud(s), it rattled loudly then softer then stopped. Almost like some loose connection would make an audible ticking sound as it vibrated and slowly softened/abated as the vibration subsided.
I am convinced this is a physical defect of some sort within the earbud which Apple have yet (and probably will not) admit.
I only hope that the next version of the AirPod pros have this defect fixed, as I do find them some of, if not the best wireless earbuds with noise cancelling for their cost.