It could be 'outside' interference, such as a generator or other local EM source and not internal to the devices. Maybe use them in another town or power source?
Wrap them in tinfoil?
Wrap them in tinfoil?

Dell Latitude 13.5" 2-in-1 Ubuntu/Win 11
Samsung Note Pro SM-P900 12.2 Android 5.0.2
Samsung S7+, Android 12
Samsung Note Pro SM-P900 12.2 Android 5.0.2
Samsung S7+, Android 12