Chevrolet Repair: high pitch whistle, magnetic saturation, rf noise

Question
I have a 1995 c1500 2wd 4.3l vortec. The truck makes a high pitch whistle. Seems to lessen when you give it gas. I have replaced the alt., coil, plugs, cap, wires and no change. I have removed the belt and started, no change. Sounds like RF noise not vaccuum. What can I check next??

Answer
Hey,

  Make sure there are no ignition wires too close to the alternator fat wire.  There could be magnetic saturation of the secondary ignition traveling on the back of the dc voltage and you are hearing it in the speakers.  Use a meter on the ac scale on your battery to check for a bad diode on teh alternator.

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