David - ""guys looking after the cars who know a lot less about electronics than we do....."
I hear that. I once brought a car back to the dealer because of some ground noise in the radio. I explained to the mechanics three or four times, that it was gound noise, and the easiest way to hear it was to turn the radio on with the volume all the way down. Every time they said: "There's no problem. I turned the volume way up and din't hear any noise." About six months later I got a recall notice because of a grounding problem in the radio wiring harness.