Sorry to bust in but I find this interesting since I have a similar problem.
I have had a problem with a whole house audio system that a radio station bleeds through the speakers and I have always thought the signal was RF interference pickup up by the AC lines acting as an antenna. However you are saying that unless there is a tuner to demodulate that signal you wouldn't hear an audio signal which makes sense.
In my case there is no FM tuner in my whole house audio system though so I cannot imagine what is demodulating the signal. What other components would be capable of demodulating an FM signal?
I have also had the radio station come through my music PA loud and clear using me as an antenna. When I plugged a cable into the mixer (again no radio tuner present in the system) I got a clear radio signal out of the PA speakers.
I will never again buy a property near any broadcast facility due to the strong RF signals present and the effects they can have on equipment. I realize it isn't the broadcast facilities fault if they are transmitting within their power spectrum but my faulty equipment (poor shielding) or possibly AC power supply makes life difficult to say the least.