What would make the outlets with a GFI have a buzzing noise?
Some GFIs have an audible alarm and buzz when they trip.
I have found that a GFI that has been painted over or corroded
stuck will cause a buzz when it is overloaded and trying to trip.
The problem is when it is painted over and seized open it cannot
trip and causes a buzz.
I would first start by having the GFI that is closest to the
problem switch replaced then check the switch again.
If you have any other questions please feel free to email