itpro, have you by chance swapped your HUs to see if the problem is specific to the vehicle or the HU? Perfect chance to isolate the problem!
I've tried separating and shielding the signal and power wires but nothing makes a difference. Using name brand Pioneer and Apple cables too. Especially since it occurs during dvd playback, it seems like it has to be internal. I haven't tried SD playback, but I doubt it'll be any different. I saw about grounding the RCA shielding, but again, that won't have any impact on internal source playback. So I guess that leaves interference coming in on powe