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Radio Noise from Alternator

The alternator in my 1992 Buick Century is generating a faint “whirring” sound heard through the right speaker of my car’s radio. I had this same problem 110,000 miles ago and at the time, my mechanic replaced the alternator because he said that sound meant that total alternator failure was inevitable. I would like other opinions before I spend for another replacement. Is radio interfereence by the alternator a serious problem?

I think what the tech was concerned about was a problem called AC ripple coming from the alternator. If a diode in the alternator goes bad it causes a higher ripple wave in the charging current. This also causes a drop in the amount of charging current the alternator can deliver to the battery so the system is degraded. If enough diodes fail it will cause various minor problems and you will have a weak battery. It shouldn’t hurt the radio though, just cause noise in the audio.

You can measure the amount of AC ripple at the battery while the engine is running at around 2,000 RPM and using a voltmeter set to measure AC voltage. Normally you should not see more than .1 volt AC. If you do then there are most likely bad diodes in the alternator.

It is a little strange that the noise you are hearing is only coming from one side of the radio. This makes me think there is something wrong with that channel inside the radio and not the power to it as both sides should be affected if the trouble was coming from the power supply lead. You can disable the alternator by pulling the connector to the back side of it and then start the car and see if that sound goes away. If it does, then the alternator is suspect. As a precaution remove and replace the alternator connection with the car OFF.

Could be a sign of a failing alternator. Or it could be a poor antenna connection. If the radio isn’t getting much signal from its antenna it will amplify what little signal it gets as well as noise from the various electrical devices in the car. If the alternator noise is the loudest electrical noise in the car, that’s what you’ll hear whether the alternator is failing or not.

You could try getting the alternator tested.

Or you can tune a weak signal on an ordinary transistor radio and see if you hear alternator noise in the passenger area. Compare the radio noise on that radio with the noise on a couple of other cars. Try the same thing a few feet from the front of the engine with the hood open. That should give you an idea whether your alternator is exceptional noisy electrically.

And, no alternator failure is not that serious a problem. It’s not a safety issue. But it will eventually result in the battery not charging and the car not starting.

My alternator is located on the right side of the engine. Is it possible for the ripple emission to be strong enough to be picked up directly by the right speaker without going through the radio circuits?