Wires acting as input and Output
Even though a wire may appear to be earthed or connected to a power supply it is easy to "isolate" that wire to use it as an antenna without trashing the basic operation of that wire for either transmission of DC power or audio. 

If an inductor of low value (typically less than 1 micro henry) is placed in the wire it will act as a blocking impedance for radio waves whilst passing audio and DC power virtually as if it were a short circuit.

1uH at 20kHz (top end of the audio band) has an impedance of 0.13 ohms so it is barely going to affect audio transmission. 1uH at 100MHz has an impedance of over 600 ohms so it will act as a decent blocking impedance for the FM radio band.

Add a capacitor in parallel to tune it broadly at 100MHz and the impedance will be even higher at RF and remain largely sub 1 ohm at audio.