Glenn, on my Danfoss BD35 based Isotherm ASU system the RFI was
unbelievable annoying.
The biggest noise reduction of all the cures I tried was given by a
simple short wire clamped to the copper refrigerant pipe where it
enters the compressor housing and the other end to the battery
negative.
I even went to the trouble of removing the plasic housed electronics
board and remounting it inside an earthed metal box.
Ferrite suppressors, power line filter and other tricks made little
difference.
The compressor is powered by its own dedicated battery.
All the HF radio interference entered the radio via the antenna, not
the 12v connection.
Hope this helps,
Klaus