| We spoke on the phone & as I said 'alterantor whine' is normally always something on the earthing side.
Have you tried moving the amps tempory?
One thing to note - How bad is the whine? On my last S I noticed a very faint whine from the rear - only audible with no music playing & when accelerating with the heater off & windows shut. I assumed it was an amp problem, but then when messing with my system noticed it was there with no power connected & even with the amp disconnected!
My new S it is there - Standard speakers & no stereo no amp - there is a VERY faint whine coming from the rear of the car & I havn't worked out where from yet | 
