A friend I've known for thirty years, but with whom I had lost contact, called me to root out a problem. He had bought a condo about 1500' from a transmitting tower that broadcast a Spanish language religious station and he was getting interference in everything. That included a loudspeaker connected to a McIntosh power amp...when the amp was turned off.

I usually have some ideas, but this stuff was insidious and I couldn't make more than a tiny bit of improvement.

The surprise was that this was happening at all, because it was an FM station. FM signals are always at exactly the same level of power but they vary the frequency of transmission to put the sound onto the carrier. AM makes total sense for such interference as AM is simply a radio signal that goes up and down in volume (i.e. power), so anything that can filter out the RF (not hard) and one side of the carrier (not too hard) will give you signal. We could not figure out AT ALL what was able to convert varying frequencies around 100 mHz into audio!