Can't hear it. But the cable microphonic is horrible

No noise floor with my unit. Sound separation is good enough for me...at least better than the OG Quarks.

No noise floor that I can detect on mine at the volume levels I listen at (75dB) over multiple devices. Nothing but dead silence. Sound seems separated well enough that I can hear multiple instruments over each other and can hear sound as it travels left to center to right of my position and just behind my ear on my shoulder. For $15usd, I don't know what more one could expect here? Seems good enough.

I only notice it with high volume and no music playing. In actual use when I am outdoors moving around or even sitting near PC fans I have never actually noticed it during music even in the quietest passages though there are some who report that they have. Maybe if I listened to classical music lying down in a quiet room I would.

I cranked mine up to max with no music playing and had the same blackness.

As for others hearing a noise floor, I wonder if that's just their tinnitus they can hear from the Quarks most excellent seal, lol (I kid, I kid). I'm just lucky my USB ports on everything doesn't seem to transfer any kind of noise as I've had noisy USB ports in the past on my older PC.

I've got a decent amount of noise floor with mine. It's not audible while music is playing. But any time they aren't playing something else I can definitely hear jt

What app do you use to know at what db level you are listening?

I measure it manually with a dedicated decibel meter. While this is harder with IEMs I am very very familiar with what 75db (average) sounds like after doing many many measurements over time on different headphones. In reality my listening would be between 65-79dB to account for highs and lows but I like to average around 75dB.

Haven't noticed it with my s21 but with other phone with type c its unbearable, you can clearly listen the phase change. I think the problem is with usb 2.0 devices.