alternator whine...oh god. I've been through this. but am far from expert. -often remedied through proper grounding of head unit or amps. Check that amps are grounded properly or have a seperate ground run back to the battery. see "ground loop" stuff on web. -may not apply to you but a head unit with higher voltage preout often helps, 4-5 volts. -bad or old battery can also be a factor. -coils may be used at the power source to amps, for ultimate solution, though suboptimal as it will increase resistance of power to amps.