the only reason I am not concerned about the alt is you have mentioned everything about anything in the dash or door moving EXCEPT the voltage gauge. The only time the alternator was mentioned when I looked back was to call the noise in your stereo "alternator noise" which is what it is called and what makes the noise but properly installed and functioning equipment will not have a problem with this noise, they are designed to work with it as its expected. Now the low voltage at idle does tell me its the alt or underdrive pullies? . Another thought, there should be a small metal can mounted to your coil with a single wire coming out of it. It is a cap that reduced noise and can cause this problem as well.
The pico fuse is supposed to be some kind of safety device to protect idunno what. It only blows during improper procedures and I am willing to bet they have a plan to replace them if/when they do blow and not at a loss either is my guess. Just try grounding the outer RCA shield while the deck is on and if the noise quits, that is the problem.
The grounds/kick panel is stab in the dark but when your chasing electrical gremlins no matter how bright your light is there is always another dark area right behind you....
