I have high hopes for this to restore the noise cancelling back to what it was with the first firmware (great!) but I suspect for many people like myself this is actually a hardware issue:
Suck on this! (LOL look at the language we've resorted to fix this on our own...)
forums.macrumors.com
What
may be happening is the microphone that points in toward your ear to monitor and adjust the NC gets gunked up after about a month of use, and then the NC is much worse as it isn't correctly tweaked by the AirPod software. And there's an objective test as well in that the Ear Tip Fit Test doesn't pass anymore. Myself, I too late tried the remedies in that forum thread and I think my AirPods have damaged in-pointing microphones. Just from normal use, I might add.
Anyway! I'll report back if this firmware update helps. And when it doesn't (as I suspect) I'll see if I can get mine replaced, and then vigilantly do the Fit Test and clear the mics so the awesome initial noise cancelling can remain.
update:
Well, 2D15 didn't do anything for me, like I expected it wouldn't.
I think if you're someone who likes to put them in and kinda twist in order to get them firmly in place, you might want to do the Fit Test once a week or so to see if the noise cancelling is degrading. And perhaps use 'blu tack' to clear out that inward pointing mic so the NC stays good. Because it was SO good initially. Now it's just crap, for me.