What causes the alternator to whine?
A disparity in voltage (electrical potential) between two connectors causes an alternator whine. The voltage difference could be caused by an incorrectly grounded stereo, radio, or alternator part. Stereo whine can be prompted by an amp, the head unit, and intermediary pieces like equalizers and crossovers. It is usually remedied by locating the source of the noise entry and re-grounding that part.
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The most prevalent form of bad alternator noise is a loud, annoying noise that continues while the engine runs. The alternator whining noise will become louder as you accelerate. When the RMPs keep increasing, such as when you accelerate, the noise will become higher in pitch as the ring gear spins faster.
Several different things could be causing this noise. The most likely cause is electrical input from your vehicle’s alternator. In this post, I will run you through all the possible causes and fixes for whining noise from the car’s alternator so you can avoid or fix the annoying sound coming from the alternator that makes driving less peaceful.
What Causes Alternator Whining Noise—and the Fixes for It?
When your car begins to make unusual noises, it is always a cause for concern. However, without knowledge of the different engine parts, these noises can be hard to diagnose. There are several factors that can cause your car to whine as it accelerates. The following are some of the causes (and fixes) for the whining noise coming from your car’s alternator.
Disconnect the RCA Cables from the Amp and Insert a Muting Plug
By unplugging the RCA cables from the amp and inputting a muting plug, you can usually identify the problem with the head unit (RCA plug with the connectors shorted together). This also removes noise from parts upstream of the amp, such as equalizers and crossovers. If the noise is gone, you should look at the other parts upstream of the amp.
Check Components Upstream of the Amp
First, attach the RCA cables from the head unit to the amp (we are assuming the presence of equalizers and crossovers between the two). Start the engine. If the noise is gone, the issue is with the intermediate parts. If the noise returns, the issue is with the head unit.
Find a Better Ground Location for the Problematic Component
Almost always, you’ll just need to find a better ground location for the problematic part. The best solution is to keep the chassis metal clean and bare. On most occasions, installers will use whatever factory bolt is available, which can work but can also cause issues.
Factory bolts are generally not a bad source, but if they are used as a ground by other electrical parts, they can be a source of the noise. If you aren’t using a new ground point, ensure your factory bolt satisfies the above criteria.
Make Connections
Place the deck on top of the amp after removing it from its mounting location. Install a non-conductive shield between the two.
Connect the power leads (power and ground) from the deck to the power terminals on the amp. Then, using very short RCA cables, attach the head unit to the amp. Male-to-male RCA gender changers are approximately the right length.
Start the Engine and Listen to Where the Noise is Coming From
Start the engine. If there is still noise, it is most likely a rare head unit problem. It’s most likely coming in via the cables. If the noise is being caused along the cable run, switching to unprotected, twisted pair RCA cables can help. Inspect your head unit for open RCA shield grounds as well, as these can be a source of the noise. Other times, you’ll need to connect the ground wire of the head unit to the same grounding place as the amp.
Use a Ground Loop Isolator
If neither of those options works, a ground loop isolator can be installed on the RCA cables. This is essentially a small box containing 1:1 transformers. It decouples (breaks) the RCA cables’ electrical linkage and supplants it with a magnetic coupling. Noise is eliminated because the music output on the RCA cables is AC voltage, whereas noise is DC voltage, which a transformer does not allow to pass through.
