This currently lies on top of our generic "in flight" logic which is based on GPS OR airspeed, as it is meant to be pessimistic about you being on the ground. If I remember right, any airspeed kicks it off (20 knots or higher). Probably 20 knots ground speed too. This has some time hysteresis as well.
It isn't adjustable in the DFG. It also won't make it into the change released later this week, which is already in stable testing.
It will need to be user adjustable - if we made it fixed at 30 knots, the guys with some LSAs and STOL planes will complain it goes off in the air. We've learned that lesson before!
There is no way it's making a pop in your headset. What is likely happening is that there is some other part of the air/ground logic that is making the pop, since they all trigger at the same time. Transponder turning on/off? AoA kicking off?