Background hissing sound only when playing

Quad Cortex Bug Reports
1

I am desperate to find a solution and afraid that there is nothing that can be done other than switching to a different system entirely. Very frustrating because I sold my amp and pedalboard that I loved to fund this.

Since I got my QC I have had this noise issue that when and only when I play, there is an awful noise (almost like a hissing, static sort of noise, or how old recordings from the 40’s have that noise in them), especially on high gain set ups (still present on clean though)

I have been through Sweetwater support several times now, even contacted Neural DSP and tried many things, including having a 2nd unit sent to me to no avail.
A secondary issue I am having is getting a very weak signal when trying to play into DAW, when I try to set input and getting the meter right, I takes a LOT of added DB to get a good reading (little yellow, not clipping). Additionally, when I turn up input it makes the noise issue far worse.

Some of the things I’ve tried so far include:
Gain staging
2nd QC sent from Sweetwater
Different Cables
Headphones
Testing unit at a different house
Having unit away from electronics
Plugging unit directly into Yamaha HS8 monitors
Global EQ
Noise Gates
Trying 3 different instruments through it (PJ Bass, Strat, 335)

What gets me is playing a plugin through scarlett 2i2 gives me perfect tones that have that same issues on QC plugin presets.

The only success I’ve seen in getting rid of the noise was when playing bass, rolling off the tone pot would get rid of the sound, but this doesn’t help much at achieving desirable tones.

2

Did you ground the QC by plugging an XLR cable to a mixer or the monitors? I’m assuming you used TRS cables from output 3/4 when you plugged directly into the monitors.

Did you have the QC plugged into a USB hub? There’s are pretty notorious for adding noise.

How far are you turning up the input gain? A strat have pretty low output, so makes sense you’d turn it up. A 335 or PJ bass would maybe have more output (depending on what pickups and how heavy or light you might play. These are some very important factors since you shouldn’t need to boost the input much at all if you play at a normal strength and don’t have low output pickups).

Do you boost the input of the USB interface much? Those interfaces have very little headroom and distort pretty easily. I feel like I generally keep the input knob around the lowest setting on these because anything higher is clipping with guitars similar to a 335 with a humbucker or PJ bass.