There's been a lot of comments on Indiegogo re electronic noise getting onto the headphone output when audio is NOT playing.
I'm a long way off from getting my Gemini so can't do any proper investigation yet but I would like to share my experience of an identical problem with a different product.
My Dell XPS13 had this problem of clicks, wizzes and beeps when it should be silent (running Linux).
Turned out this happened when the sound card entered a power saving state almost immediately after finishing playing (emptied the buffer). I suspect that at that point, parts of the circuitry are powered down and any electronic balancing/noise reduction techniques ceased to function.
The fix was to disable that power saving feature, incurring a very minor battery penalty.
I would suggest that is where folks go looking for a solution with the Gemini first, although a battery penalty might be more severe with a smaller device so it might be something that's worth living with.
HZ