EDIT: found out that when I put my amp in bluetooth pairing mode it stops. Sound also comes out the speaker itself. So it's something internal for sure
I have a CODE 100C and when I connect it to my interface with the HP out (or even the fx send -- or even when using the HP out as a HP out) I have this high end hiss/artifact.
Here is a recording of the sound: https://youtu.be/a9mjRFiqVX0
obviously it's not as loud as in the video.. but it's still there
Recording with the HP out is the best way for me to elimante latency, but the sound quality is just bad. Also with USB I can't get acceptable latency..