GS300_1996

I am trying to install my avic d2 using preamp output with factory amp. all works except the whining noise.

Anyone know how i can isolate that? can I do it this way at all or I will just have to bypass the amp and get another amp for sub?

I have he wiring diagram for the system and it looks feasible.
Also anyone know how the isolated wires work?
Feed speaker wires from the radio going to the amp are wrapped in gray with another wire from radio. Is this grounded or something or there is some other thing in radio hat suppresses noise?

Thanks

I TRIED TO SEARCH FOR INFORMATION BUT THERE IS NOTHING I COULD FIND REGARDING THIS.......