He could change the type of fence charger. I have one which uses a
continuous HV charge (with current limiting of course) and it works
quite well and causes zero QRN.

Hi Bill, I have a homebrew one with a capacitor discharge into an auto
ignition coil. What kind of diode and filter cap. specification do they have
on the DC version you use? I would guess it is hard to let go of the DC
version:-)
73 Gary N4AST