My nans escort as developed a fault where when you turn the headlights on to any setting their is a droning noise sounding a bit like a fire work or a bomb dropping which i believe is from the door open warning buzzer does this with door open or shut engine on or off no matter where key is ignition etc. Only thing we've found is that it only does it when interior is switched on any other time the noise is really faint but still there.
Thats all the info i can think of please ask question if you need too,
Cheers Andy

 

Sounds like a leaky diode in the sidelight/warning buzzer, or it's circuit, not uncommon
tabetha