There are different combinations of mains isolation transformer wiring, I would suggest trying the stock standard wiring first,
before doing any dangerous earth/ground cuts

If that's a fail, then it's time to try a pair of input signal transformers
If that's a fail, then the electronics in the active/powered/amplified monitors need attention
and yes some Ground Loop Hell may be at play here too
fwiw before doing any of the above, check and test ALL the signal cables FIRST, in a medieval fashion if necessary,
i.e. pull the lot out and start plugging till you hear the offending racket