Well, I slammed the trunk, the back doors, the dog (just kidding), tried reseating all the plug wires I could get to in a semi-warm engine, all to no avail. I will check the rear defroster gridlines when I get home tonight. But how in the world does a broken gridline cause my radio to pick up "spark noise" ?

I think I may have answered my own question, according to the owners manual:

"Diversity Antenna System

Your AM-FM antennas are located in the front
windshield and rear window. Be sure that the inside
surfaces of the front windshield and rear window are not
scratched and that the lines on the glass are not
damaged. If the inside surfaces are damaged, they could
interfere with radio reception."

cajun