Do you have a spare head unit to swap in and check? Kind of a PITA, because the connector probably wouldn't be the same...I did a test using the high level input, and the same result - so no joy there either.
I also tried to swap the RCA cables again since the last time I did that was before I redid the ground connection. Same deal, no change. I even tried one channel at a time, swapping connections back and forth, to try to identify a bad channel. The static is the same no matter what I do.
On a whim I wired the + power connection directly to the battery to bypass the PDC. Same deal.
I've rechecked all my wiring to make sure I didn't cross something up, but I can't find anything.