your going to have to draw a mock up of how you have things connected, as I am interpriting it, you have a 3S lipo battery, and are powering 1 device off the 3S and one off the 2S tap at the same time?
Or if its via a switcing converter to step one up or down, some idea which would be better.
All high impedance nodes act as antennas, its only via sheilding the wiring these nodes run through to the lowest impedance reference plane of your input device that you stand a chance.
If your sheilding just goes to an isolated case ground that never actually links up with the system ground it wont help you out there,
A way to test if external interference is your issue would be to disconnect the output of the F4, and hard short out the signal to the GH5 there, see if the noise is gone, next leave it open and see if it gets worse, this will help you narrow down what role the F4 is playing in this problem.