HELP NEEDED! Hum/Crackling Behind Playing

Hey all. Hoping you guys and gals can help me out.

I play bass through the Quad Cortex. It’s dead silent when I plug in, but as soon as I start playing there is a hum/crackling/fizzle behind the note I’m playing. It almost sounds like a grounding issue, but I have 5 basses and it does it with them all. Plugged straight into my regular amps, all basses are also dead quiet. My assumption is that it has to do with the power, but I’m unsure. I switched to the QC from a line 6 helix, and the helix was super quiet as well. Any help is appreciated. Thanks.

how are you monitoring this? Headphones or speakers? What else is connected to the QC? Are you using the factory power supply?

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I have used it with headphones and plugged into my QSC GX5 that then connects to my GK Neo 410. The only other thing connected to it is my expression pedal. I get the fizzle/hum in both situations.

Yes. Using the QC power cable.

Hmm, mysterious.
Have you tried the Ground Lifts on the QC?
I’ve never seen those make a difference personally, but it’s all a process of elimination

Yeah I tried that as well. Made it worse.