I noticed this during my first outing with my '14 but didn't pay it much notice.
I have a minor whine coming across my speakers when the volume on a non occupied frequency is turned up just a bit. From old days I would think broken down ignition wires or resistor plugs worn out.
Same thing on the Mirage? Or is there something else I should be looking at? Can the radio actually start to whine/hum with age? I'm going to replace the plugs but wasn't planning on doing the wires.