Audio Systems: Humming/rumbling sound from speakers when headlights are on, chrysler voyager, ground loop

Question
Dear Garry,

My 1997 Chrysler Voyager's audio system's speakers make a loud humming/rumbling sound when the car's headlights are switched on while the cassette is playing. Any idea what it could be? (The noise does not occur when the radio is playing, only the cassette).

Answer
The cassette deck is picking up a ground loop from another circut in the car. Sources can be poor ground strap connection to the back of the radio, or more likely failing headlamp switch. Dodge products are famous for melting the headlight switch.  Check that before it fails completely.