Did you swap all xlr’s including those from whatever DSP the venue is using to the amps?
Did you check the speakon cables from the amps to the speakers?
You need to isolate the exact cause of this issue so what I would do is plug the unit directly into some powered speakers/monitors and see if the issue goes away. If it does then the issue is either from the DSP to the amps, or the amps to the speakers and you should ask the venue to have their sound engineer look into it.
If you can reproduce the issue with the unit plugged directly into speakers then swap out the xlr’s again. If it still happens then it is probably the unit.
@Rbarry007 - If this persists with different cables and speaker configurations, please contact our Global Technical Support team. They will be able to assist.