So as to stay on topic, I will only address the (true wireless) BT20 model. On my 2-pin version, I always use a popular quad driver. On the mmcx I mainly use the ibasso IT01, but I’ve also used the Pioneer CH9T. If you let me know what IEMs you’re having the issue on, I’ll be happy to try it for you (all my gear is in my profile). I can try the T2 if you want me to (although the fit of the T2 is so finicky it may be an instant fail). Note that both the IT01 and CH9T aren’t hybrids. Maybe that’s what’s causing your issue? Or perhaps an impedance matching issue? Anyways, I get zero hiss on all 3. However, as I mentioned before there is a barely perceptible ‘white noise’ static sound, but only when the music is paused. I get hiss on a few off my ultra sensitive all-BA wired IEMs (when connected to some sources). That’s an actual ‘hisssss’ sound, and it’s present all the time. The static sound in the BT20 is like a ‘shhhhhhh’ sound, like tuning a radio or old school analog TV static/white noise. And despite it only being present when the music is paused, the sound goes away after 5 seconds. I think it’s a sleep/power saving function. This is not unique to the BT20, as I’ve heard the same barely perceived ‘white noise’ static sound on other Bluetooth gear. I don’t know if the BT20 ‘static’ is the same thing you’re hearing (or referring to as hiss). Hope that helps.