Hello beinghuman,
I fly helicopters and I've also noticed a tendency to overeact of the more sensitive modern VSI. This is happening apparently when there's a brutal change in static atmospheric pressure; for instance when we cross the edge of an helideck (brutal change from "in ground effect" to "out ground effect" ) or in turbulences. There's an hybridization with a vertical accelerometer to the VSI on this equipment, but it doesn't seems to improve much the indication.
If this assumption is correct, should it mean that the pressure near the static ports in a ground effect air flow, is lower than atmospheric pressure ?