Are you sure the intefering signal is coming from the cable? You can't hear a radio signal it has to be tuned by a tuner to convert it to something you can hear. A radio signal picked up on the coax usually shows up as distortion in the video not audio.
That's not entirely true. If there is a transmitter close by that has a very strong signal it can induce into many things. You don't necessarily need a tuner. As an example, many years ago, when I was a telephone repairman, I went out on a trouble call for radio over the telephone conversation. We had filters for just this purpose. One way was to put capacitors in a particular array at the protector where the line connects from the pole to the house wiring. We also had a special filter that we could use which was a lot more advanced, but quite expensive. None of these fixes worked. I was out on again on a several time repeat call, this time with my boss
and his boss. My bosses boss thought I wasn't doing enough to help this lady out. I asked the lady to open her refrigerator door. She did and, BOOM, It was like a loudspeaker. There was religious music coming out of it. The radio station, one of those religious ones, was transmitting way over its assigned power level. A report was made to the FCC and we never heard from this lady again.
