I have noticed a feature for the premium sound that may go unnoticed to everyone.
My patrol uses a jay car speedo corrector but at very low speeds it has a habit of occasionally the speedo jumping up to over 200kph, when it does that the volume of the sound system increase in level till it settles back down to realistic readings.

Not sure on the falcons, but my old vy commodore had speed sensitive volume. Would turn itself down when you slowed down and vice versa.