engine whine

Everytime i put a 4 channel amp into a vehicle i end up with engine whine.  When i unplug one set of rcas, the noise go's away.  The noise is only usually there when both pairs of rcas are plugged into the amp.  The power wire is run down the opposite side of the vehicle that the rcas are.  The deck, amp, and any other components are grounded to the same location on the vehicle- usually the floor of the trunk using a lock washer and a bolt-the paint is cleaned off ofcourse.  i have tried everything.  i even tried grounding the components directly to the battery and there was no change.  The amps are mounted to wood and not metal.  The only thing that seems to cure the problem is a ground loop isolator.  However, this is only masking the problem, not solving it.  Does anybody have ant answers or ideas?  Much appreciated if you do.

                                                                                          thanks, Rich

OK, now you're down to ignition system noise.  This is where it gets really fun.  Could be bad spark plug cables, cracked or worn out distributor cap, a cracked spark plug, bad engine ground strap, bad coil, bad ground on the engine control unit (computer), bad brushes in teh alternator, or a faulty voltage regulator.