Receiving AM radio through household wiring
the LC part comes about by capacitive coupling to ground that happens naturally when the wiring comes close to a piece of grounded metal, and the fact that even a straight piece of wire possesses a little bit of inductance. If the incoming AM radio signal is strong enough, even a badly-tuned LC tank circuit coupled to a poorly-fabricated cupric oxide contact diode will receive and demodulate enough of the signal to feed it into an incompetently laid-out and assembled ground system in a building, and hence bleed it into your audio feed.
The transistors in the first-stage preamplifier of a sound system can also act like diodes, and demodulate RF interference signals leaking into the circuit from poor grounding.
I know this from personal experience, having had to fix this problem in a church sanctuary in which the hearing aid transmitting loop encircling the room acted as an efficient radio frequency loop antenna, picked up the sunday morning (!) "Metallica Meltdown" show from a local AM station, and bled it into the ungrounded mic feeds leading into the sound system. we'd be sitting there in the Moment Of Silence and heavy metal headbanging music would be faintly playing out of the PA speakers...