I think I know what you are talking about....sort of like yawning, but also flexing your ears and raising your eyebrows?
I do this do normalize the pressure, I think that yawning opens eustachian tubes, which normalizes pressure in the ear (not sure which part tbh), and the phenomenon you experience as volume increase may be changed in resonant geometry of ear canal?? OR outside noise coming in due to airways opening up....yeah our bodies are weird
I use triple flanges as well, and I find that doing the yawn/ear stretch helps normalize the position of them (too deep results in stuffy fatiguing sound), and also normalized ear pressure, and makes them sound wicked good