DMR E50 connection problem

I am trying to setup my DMR-E50 to allow recording from my cable box. I have the cable box connected to the recorder via Scart and also the RF output. I have tuned the Panasonic recorder to the RF output channel 38 used by the cable box.

When I record the RF output I get a picture recorded but the sound is just White Noise. Can anyone advise me why this might be as it is driving me mad!!