Noise Problem Has Me Stumped, DS18 Amplifier, Stetsom DSP

Ok so a few months ago i installed a full system in my 04 dakota. A DS18 4 channel amp powering a single set of two way components in the front doors, stetsom DSP being used as main crossover for the components only, im using another 4 channel amp with a blown channel for my bass amp running a single 8 inch sub, and the HU is an older pioneer single din.
Im using the front output from the pioneer through an RCA splitter to send signal to the DSP and to the bass amp separately so the DSP only controls the door speakers and the bass is controlled from the radio directly.

Everything sounds great except for the smallest amount of hiss and also a barely noticeable alternator whine when the engine is running. I have done EVERYTHING that i can think of and nothing has had any effect. Ive done the big 3 upgrade with wire far bigger than necessary for under 1000 watts of amplifiers would need. I have tried several new grounds for the radio even going as far as to run a ground down to the same spot as the amp to eliminate any potential ground loop. I even broke down and made a 100 farad capacitor bank to connect directly to the amp with no effect at all.

Neither the hiss nor the whine get louder as i turn the volume up which tells me that it's coming from the amp directly and not something that is in the actual signal but if i unplug the RCAs from the amp the noise goes away. How does that work if the noise is a product of the amp?

Is there something i can do to the amp that might fix this? Ive tried grounding the RCA shield to the amp ground and that made the noise 10x louder, did the same behind the radio with similar results. Its also not being induced by any sort of electronics or blower motors, etc. The only other thing i can think of is maybe it's the alternator itself. Truck has 130k miles on it and i could see the diodes being worn out but i put my oscilloscope on the line from battery to alternator i dont see anything other than a reasonably steady voltage around 13.8v at idle.

So im just out of ideas at this point. Anyone have any creative ideas that have worked for you? Im willing to try anything that sounds plausible. Thanks in advance.

Had a similar problem once and ran my constant power wire from the radio directly to the battery under hood, worth a shot

I guess it's worth trying even though im almost positive the radio doesnt have anything to do with it. Im well aware of the typical pioneer noise problems but this definitely isnt bad enough to be that.