I use the aux sends on my Mixwizard for monitor sends. Normally I just have one mix. I get a lot of noise out of my powered monitors. Powered mains (using same power source as monitors) are clean and quiet.
If I switch speakers (connect mains to snake monitor feed and and monitors to the snake main feed) the speakers first connected to the monitor feed become quiet as house speakers, and the house speakers now connected as monitors become noisy.
Lifting the electrical ground on the noisy speakers significantly reduces the noise.
All speakers from JBL PRX600 series
Monitors are 612m and 615m
This is how I connect with monitors on the stage:
from mixer - TRS male to XLRm (cable) to snake
stage end of snake - XLRm to XLRf (cable to monitor #1)
XLR cable from monitor #1 xlr out to monitor #2 xlr in
It seems to me that there is something in the connectors and/or cable/snake combination. I have 2 MixWizards and the problem exists on both.