AirPod Pro 1st Gen Hissing only in Transparency mode

I had problem with my AirPods Pros hissing but only in transparency mode. Not when ANC turned on or off. The solution I found was different than any I had seen posted. It turned out I had inadvertently inserted one of the rubber ear cups 90 degrees off from the axis of the oval. My guess is that this distorts the two air vents cut into the cup which somehow affects the blending of outside sounds with the AirPods sound. Distorting these vents or otherwise blocking them seems to affect transparency mode. I went thru the recommended regime: cleaning of vents, reset, etc. Then I stumbled into the actual solution. Something to add to the checklist