Hey! Just had a read and seems that the quad cortex should be grounded using the XLRs to your monitors.
I’ve found this thread from a few years ago of someone having a similar issue - may be worth looking to see if you have a ground lift switch to try as that’s quite common.
Do you have any alternative power supplies too? I know I’ve experienced grounding issues when using headphones exclusively with original power supply but using a Walrus Audio Canvas HP sorted it.