Re: Noise occuring only after installing second set of RCA's..
I have the same problem with my Pioneer 6400. One set of preouts hooked up, no noise... add a second set, get noise. Doesn't matter which set comes first.
I've redone the grounds over and over with no change. However.. remove the HU from my (metal) dash and the noise goes away. It's gotta be ground related and it's a friggin Pioneer thing.
My nephew solved his engine whine (also Pioneer) by making up little inline cables that let him ground the RCA shield right by the HU. I'm gonna try that.
1999 Buick Park Ave Ultra
Head Unit: JVC KWHDR720
EQ: Audiocontrol EQL
Front Stage: Hybrid Audio Technologies Imagine 5.25 mids, Morel Maximo tweets
Sub Stage: Boston G3 10", 0.5 cu ft sealed
Amp: PPI Phantom 900.4
Rear Fill: Boston SE953 6X9's