Buzzing Sound When Shut Down - XLR Cables

I listen in the bedroom using Presonus Eris 4.5 monitors. To date, I have been using 1/4" TS → RCA unbalanced cables from the MFX pedal to the Eris input. No issues at all using any MFX pedal, including the QC.

I recently had to do some testing on another MFX pedal, so bought some XLR → XLR cables, not top level stuff but acceptable quality. Using the QC, I now get a significant buzz in both monitors when I shut down the QC, with monitors still on.
As soon as I start the start-up sequence on the QC, sound goes away.
If I place the QC in stand-by mode rather than shut down, there is no buzz.
I tried a different power supply, still had the buzz.
I have tested different MFX pedals, some fairly high level pedals - no buzz from any of them.
I updated from CorOS 1.4 to 2.0, no difference, still get the buzz.
There doesn’t seem to be any setting on the Eris rear panel which should affect this noise.
I went back to the TS → RCA cables, no buzz.

Is there anything unusual about XLR cables that I should be doing different, noting that this doesn’t occur on any other MFX pedal?

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In case anyone else looks at this post looking for answers, somehow I stumbled onto this thread:-

Ground loop noise when powered off - emitted via Out 1-2

FYI. This is normal; they all behave this way due to how Neural has chosen to execute the grounding.

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Thanks for this reply - if nothing else, it has set my mind at ease.

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hi @DunnyDaw , are your xlr connectors painted or plastic made? take a look at this:

Loud buzzing from amp after powering off QC