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Noisy Alternator

Alternator noises are usually mechanical in origin, but a high, soft whistling sound may be produced by an alternator that is overcharging because of a faulty regulator diode. The same sound may be heard if there is a shorted diode that is placing abnormal electrical strain on the alternator. Some alternators make this sound when operating normally at maximum output.

Alternator mechanical noises are usually the result of misalignment between the V-belt and the pulley, a loose or broken pulley, worn bearings, or a bent rotor shaft. Check for bad bearings by removing the V-belt as described below and rotating the alternator pulley by hand. If the pulley or shaft seem to grind or grate, replace the alternator.

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