Comment by vachina

I tried everything. Cleaning out the vents, cleaning out the grilles. The failure is not in the reduction of the ANC, but outright amplifying ambient bass into my ear. This is why I got them replaced by Apple, which in their diagnostics confirm there were issues with the ANC.

In any case these workarounds are moot, because my $20 Chinese ANC earphones work (until today) without all these fussing around at all.