As shown in the above photo, the voltage generated from the alternator while the engine is running is just 12.69V. This is the clear message that the alternator is dead. But the dealer said the car is is perfect condition. Always trust but verfiy in any used car purchase inspection.

From below, one and two are the typical symptoms that the alternator is failing. Please take the car to your favorite mechanic for inspection. Of course, there could be other causes generating the similar noise.

1. High frequency booming noise
2. Metal grinding mechanical noise
3. Low battery warning light on your dashboard (blinking dashboard lights, dancing gauges).

For three, the alternator has already been dead. The car is running off your batter and depending upon your battery capacity, the vehicle will stop anywhere from 10~ 60 minutes after the low battery warning light on your dashboard. In this case, please park the car at the nearest safe location, call for road side emergency help and have your mechanic inspect the vehicle.

If your car has high mileage and worried about the alternater malfunctioning, you could have a spare alternator in your trunk. Any garage mechanic around the nation will easily replace the alternator for you.