Ok from what I understand most alternator whine is caused by ground loop problems, of the head unit seeing a better electrical potential to ground via the RCA sheilds rather than its own power supply ground.
Since the alternator is essentially an AC to DC converter, there is still some ripple in the DC coming out of it. And when the RCA signal cables are used to carry DC voltage (as a partial ground to the head unit), as well as the AC audio signal, the ripple is carried on the RCA cables, In the form of a slight voltage variation, and is fed into the amplifer, where it is audibly heard through the speakers.

Now, has anyone considered using diodes to Isolate the ground return path properties of the Rca sheilds? In other words, blocking the RCA shields ability to function as a ground to the headunit. Just a thought.

Let me know what you guys think

George