OK, finally fixed the alternator whine noise issue!!!

Installed a high/low converter on the output speaker wires and removed the output RCA plugs. That fixed everything. Perhaps the output RCA is somehow picking up the interference from the speaker wires on the Fakra cable.

So after trying ground loop isolators, power line filters, and high/low converter...I could've applied all that towards an AudioControl LC6i.

Oh well, next time. I'm just happy the alternator whine is gone and I can move on to upgrading the subwoofer to finish up the project