Okay, I've taken some additional steps since posting this, including bringing it down to an independent car audio shop I know I can trust.

According to them, it's either the sled connector on the back of the unit, or the sleeve connector inside of the car causing the crackling. I don't have a way to verify which one it is, but according to them, when you press on the left side of the face plate while it's crackling, it stops doing so.

Anyway, are these pieces available as stand alone purchases from anywhere?