I've been chasing this problem since I installed my system a few months back and I've finally had enough...

Setup (03 G35 coupe):
-Stock bose HU (has clean line level signal)
-Arc 500.1 powering single dayton audio HO 10"
-US acoustics 4085 4ch bridged with 2ch for front right and 2 for front left
-CDT audio 6.5" woofers in doors and tweeters in stock location (on door near pillar) with crossovers
-stock speaker wiring for front speakers
-bose amp plug was replaced with an adapter to plug all the wires directly to new amps

Everything sounds fantastic when the ignition is on but engine isn't running. Once engine is started the drivers side speakers and sub are fine, but the passenger side tweeter and woofer get a horrible buzzing/hissing sound. It is not rev dependent. It is loud enough that it takes 3/4 volume to drown out, and the sound does not increase with volume. It is relative to frequency because the hiss is louder in the tweeter and it decreases as I lower the frequency range via amp or crossover.

I checked my RCA's, swapped side to side, relocated grounds multiple times, put a new ground on HU body, tried different amps, moved power wires around and RCA's to try to limit interference as well as door speaker wiring and crossovers. Just can't seem to get rid of this pesky noise. The speakers are not blown (swapped side to side to make sure). What could it possibly be that would only cause the passenger side to hiss?

For reference I followed this: How To - Car Stereo - In Pursuit of a Noise-Free System: The Ten Commandments of Noise Prevention
as well as various write ups on here and other audio forums.

I'm stumped and getting really frustrated because I've torn everything completely apart countless times trying to fix this issue. Any ideas? An alternator grounding issue would cause everything to hiss right?