... after the second exchange APPro worked well, there is now on one side again a unpleasant dull noise when walking/running: the "pass" test has failed since then. It's like I assumed some time ago:
Apple has apparently found a way to counteract the impact sound on the inward-facing microphone. If that fails, the footfall sounds (as in usual inEars) again audible, as in my exchanged. The seal test ("passtest" about settings, etc.) is then also negative, so an indication of the defect.
It is clearly a design flaw that affects the (error-prone) inward microphones. Please note - you hear it on the always negative "Pass" test (under Settings Bluetooth APPro ...) and the "rumbling" noise (so-called footfall - bone conduction) by the "inner ANC" yes (if they work) should be balanced.
Meanwhile (after a little more than 2 weeks) the other inward micro is also defective: step sound is transferred and the "pass"test fails ... After the second exchange airpods, I assume that it is a design-related error prone, which is common and only not noticeable to those who are accustomed to inEars step sound, Doing little / no sport with the APpro (then the bone-conduction transmission is even more detectible/annoying).
As already described, this can be verified by the "Pass"test, which always indicates a `defective seal` in the case of defective (inwardly directed) microphones that "pick up" for this test . Many people think that it is due to the silicone plugs, but in many cases it will be a hardware defect ...
The more that you try and give Apple feedback, the sooner they will tackle this constructional flaw.