I installed a new 32 bit board (2.43.9) on my legacy handheld because my old 32 bit was damaged I didn't changed anything with the balance. Now I have a hum on all motor. If I reducing the PIDs untill there is no noise the motor do not hold the GH4.
is the motor power and battery voltage same as previously? And other settings. If you just change the board, you should be able to use the old settings (basic setup needs to be performed though)
On the newest beta fw 2.44b8 Gyro LPF works a bit different and helps to noise from motors on encoder gimbals at least, did not test yet without encoders though.