RF getting into audio of TS-440SAT
 

I have been struggling for some time to get RF out of the TX audio on
a TS-440SAT when in data mode. I have ferrite blocks everywhere;
power lead, 13 pin audio lead, aerial feeder, data control cable.
Sometimes I seem to cure it then it returns. Checked every grounding
screw in the rig, checked all internal connectors. Fitted isolation
transformers on audio. It stillcomes back. Does anyone know where
the weakness is in this rig?
Richard G4BBH