I have a quasi-hypothetical-theory...
Your mic cord is coiled.
The voice coil in the mic is coiled.
When you stimulated the coil of the dangling(assumption on my part) mic cord with movement by jumping around in the electro-magnetized environment of the Jeep chassis, it created current within the coil.
That energized coil, in close proximity to the mic, stimulated the voice coil of the mic.
So, the crackling mic is the induced current from the cord acting upon the voice coil of the mic, thus, moving the diaphragm and creating sound.
Keying the mic grounded it out.
The idea is likened to the workings of an ignition coil.
A primary coil is energized which energizes a secondary coil. There's no physical connection(continuity) between the two coils.
Why wasn't the sound noticed earlier?
Coulda been it was over-ridden by the household's normal aural ambience or, around midnight...
Last edited by funfred; 05-23-2014 at 11:42 AM.