ground loop eliminator might help, but it's not a gurateed thing in my expereince.
theres alternator noise wehnthe stereo is off toally? hmm.. .that's an odd one, maybe the power is coming close to the actual speaker wires, instead of the rcas, but if you ran them along withthe rcas then that's not a good thing... the best to do is run as far away as possible.. if you haveto cross them, make them cross at 90 degree agnles.
__________________
This Space for Rent