Quoting Matthias Schönborn :
> Hello list,
You have a ground loop in your system.
First a warning, whatever you do: do NOT disconnect any earthing pins from
any equipment to defeat the loop. Doing such things will put you and your
equipment at danger.
You can try a few things, like connecting your laptop PSU and amp power to
adjacent terminals. This can help if your laptop PSU is earthed.
The best solution (and the one which works almost every time) is to use a
transformer to isolate the laptop and the PA system. This can be in the form
of a specialized transformer isolator (available usually with RCA-RCA
connectors) or a stereo DI box with a ground lift switch.
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