How to Fix a Grinding, Squeaking, Whining or Knocking Alternator

Faulty alternators make different kinds of noises. A noisy car engine is sometimes a sign of a bad alternator. What are the causes of these sounds and how can they be fixed?

Loose belts, loose bolts, damaged rotors, worn-out bearings and bushes, and low-bearing fluids are some of the reasons why an alternator makes noises. Ways to fix this problem include lubricating the bearings, replacing damaged and worn-out parts, and tightening loose bolts and belts.

Alternator Noises

Different kinds of noises made by an alternator, the most common of them include:

Grinding Sounds: When the alternator makes grinding sounds, it’s often because of a belt that’s loose and moving around the engine or a flap that is broken and hitting other parts of the engine.

Squeaking Sounds– a squeaking sign is often a sure sign that your alternator is faulty. You may sometimes still hear it even after you have turned off the alternator pulley and car engine. This squeaking would typically get louder as the engine reaches higher revolutions per minute (RPM)sign that an alternator is going bad.

A Whining Sound: This sound starts as soon as you turn on the engine and gets louder as the vehicle accelerates. It is whiny, high-pitched, and hard to miss.

Signs of a Bad Alternator

Different parts of the car make different noises when damaged; for instance, a clutch pedal squeaking could be a sign of a worn-out clutch disc. Likewise, a bad alternator would either whine, grind or make knocking noises. This means that diagnosing a bad alternator isn’t a difficult job. It’s something one can easily DIY.

Also, the job of an alternator is to power the electrical components of the car, so when the alternator is bad, the electrical parts of the car will not function properly. When the alternator goes bad, you will notice that there will not be sufficient power in the car to power all the electrical components.

This means that the battery will start to die too quickly. The headlights will be dim as there won’t be enough power in the car to power them properly. The check engine light will come on and the car may not be able to power on quickly because there’s not enough electrical power to power it properly.

Top Causes & Fixes for Alternator Noise

Here are the major causes of alternator malfunction and simple ways to fix them yourself

1. The bolts are loose or broken

Your alternator needs to be properly bolded down to the engine, if not it will make very loud noises whenever you try to move the car. When your alternator bolts are loose, you will hear some rattling from vibration in the engine. An alternator with loose bolts also moves around, making noises as it moves. Loose bolts often happen in a car that is not properly maintained.

Fixing this problem: Always tighten your bolt over time as they can become loose with use. If you think your bolt has become loose, use a socket wrench to screw it back on tightly. However, you must be careful not to over-tighten it.

In case of a broken bolt, you’ll have to replace it.

Step-by-step Guide on Bolt Replacement:

  • Disconnect all electrical wires as they may potentially have power running through them.
  • Disconnect the belt
  • Remove the broken bolt
  • Bring out the alternator, and inspect the hole in the alternator where the bolt goes, find out if there’s anything in the holes that may have led to the breaking of the bolt. If there is, take care of that first
  • Replace the broken bolt with a new one and reinstall the alternator

Here’s a good video tutorial:

2. Worn-off alternator belt

If your belt is old and no longer tightly wound, it will start to emit worrying sounds from the alternator. Loose belts also stand a chance of hitting other components, causing a loud vibration in the process. You’ll know your alternator belt is loose if it makes a screeching noise whenever you start up your car.

A squealing noise when the car starts or accelerates could also be a sign of a loose belt. A way to avoid problems with loose belts is to always replace your alternator belt when a replacement is due. Trying to recycle an already worn-out belt will make it too loose and stretchy, eventually leading to more complicated car trouble.

Fixing this Problem: A loose alternator belt will need its pully tightened. For this, you’ll need to use a socket wrench to tighten the bolts on the belt’s pulley. A belt tension gauge can also be used for this job if you have one available. Make sure your engine is turned off while working on your alternator belt.

Step-by-Step Guide for Fixing Your Alternator Belt:

  • In older model cars, alternators have fan belts that have to be adjusted once in a while
  • Loosen the bolts then tighten the adjuster until the belt stops squeaking
  • If these belts are too loose, they make squealing sounds, yet if they’re too tight they could damage the car’s alternator, bearings, and water pump.
  • Modern cars come with tensioners that automatically tension the belts but over time they could wear out.
  • In such cases, replace the belt and the tensioner especially if you have used these for over 7 years.

..and here’s a video of how to fix the squeaky sound:

3. Squeaky Bearings

Alternator bearings are susceptible to wear and tear. If they have grown old, they might cause noise in the alternator. You will find your bearings between the stator and the rotor. They are small metal discs whose job is to spin the rotor and hold the stator in one position. Worn-out bearings cause very high-pitched noises. Bearings need to be lubricated often to avoid premature wear and tear.

Fixing this problem: The only way to fix a problem with your alternator bearings is to either properly lubricate the bearings if it’s a lubrication problem, or replace them if the bearings are worn out and damaged. Use a socket wrench to remove the alternator from the engine. Bring out the old bearings and put in a new set. Put back the alternator and alternator belt. If your bearings are not worn out, simply use a grease gun to grease them up properly and the noise will be gone.

Step-by-Step Guide for Replacing Old Bearings:

  • Clean and lubricate the screws on the alternator to remove them
  • Use a socket wrench to undo the pulley
  • Remove the alternator
  • Loosen the screws on the alternator
  • Find the two bearings and remove them so that you can see the part numbers on the old bearings, that will help in ordering new ones.
  • Inspect and clean the rotor and slip rings
  • Install the new bearings

See how to replace a noisy bearing in this video:

4. Worn-out brushes

Brushes and bearings work together to generate electricity. Just like with the bearings, when brushes are worn out or become loose, the rotor shaft gets misaligned, and they start to make a distinct grinding sound. Other common signs on worn-out brushes include dim light, empty battery, slow cranking, and seized rotor. When you fail to lubricate your brushes properly, they start to overheat and get damaged.

Fixing this problem: The only way to fix a problem with your alternator brushes is to replace them. Use a socket wrench to remove the alternator from the engine. Bring out the old brushes and put in a new set. Put back the alternator and alternator belt.

Step-by-step Guide on Replacing Worn-out Brushes:

  • Disconnect the car battery
  • Uninstall the alternator
  • Open the alternator and unscrew the brush box
  • Pull out the old brushes and clean the brush housing and slip rings
  • Install the new brushes

See how to replace worn-out brushes in this video:


5. Low fluids on the bearings

Your alternator will produce a squealing noise when low on the grease that is meant to keep it lubricated. This is because friction occurs when these fluids are absent. Fluid levels often decrease with seal leaks. Low fluids could also cause engine overheating and other engine damage.

 Fixing this problem: A quick fix for this problem is to replace the seal.

Step-by-step Guide on Seal Replacement

  • Use a socket wrench to remove the alternator
  • In many cars, you may have to uninstall many parts before you get to the seal.
  • Remove the alternator, pulley, belt, and any other necessary parts depending on the car model.
  • Bring out the damaged sealsand replace them with new ones.

In this video, you’ll see how to DIY your seal replacement:

6. The rotor is damaged

A squealing sound coming from your alternator is often a sign of rotor damage.

The rotor constantly spins to create electricity; so when it is damaged, the shaft could lose its alignment. When this happens, the parts rub against each other, causing some noise in the alternator.

Fixing this problem: Buy a new rotor, one that is compatible with your alternator.

  • Use a socket wrench to remove the alternator from the car engine.
  • Take out the old rotor and put in a new one.
  • Then reinstall the alternator belt.

Should You Drive a Car with Noise in the Alternator?

You should try fixing the noise in your alternator as soon as you notice it. It’s important to do this because with a faulty alternator one always runs the risk of running out of battery charge. A dead battery could have you stranded in unexpected places.

Furthermore, driving around with damaged parts in your car’s alternator could cause more damage to the car, which may cost a lot of money to fix.

How to Prevent Alternator Noise in the Future

The phrase, prevention is better than cure, could not be truer for cars. It always costs a lot less money to make sure that your car is properly maintained and the parts are in good condition, as opposed to fixing and replacing parts. Here are a few tips for making sure your alternator stays noise free always.

Have a Strict Maintenance Routine: You should make a habit of regularly inspecting the components of your car engine, looking out for any parts that might need lubrication or changing. Spotting these kinds of problems as soon as they occur can help prevent bigger car trouble in the future.

Keep Alternator Clean: Cleaning the outside of your alternator so that it’s free of grease and grime, debris, and dirt, would help to keep it damage-free. A clean alternator stays cool and functions properly, while dirty alternators could cause the engine to overheat and get damaged after some time.

Get a Good Quality Alternator: Low-quality alternators are prone to constant problems. So if you find that you keep having to fix your alternator, you may want to look into getting a better-quality alternator. This might cause you more money to purchase but it’s cheaper in the long run.

Schedule Regular Alternator Inspections: Set out time annually to inspect your alternator for any problems. Carefully check the bearings and brushes, belts, and pulleys for any signs of wear and tear. Alternator belts, for instance, should be replaced once in 7 years max. Also, replace other parts as soon as you see them show signs of damage

Always Grease Up Your Bearings: Your car bearings need lubrication to function properly, so make sure you properly grease up these parts during your car maintenance.

Keep an Eye on The Voltage Regulator: If your voltage regulator is damaged, it could cause your alternator to go bad. A voltmeter can be used to tell when your voltage regulator is bad, but a faulty regulator will also show other signs such as dim headlights and an empty car battery. Ensure that this part is often inspected during maintenance and replaced when showing signs of wear to avoid an unexpected breakdown in your alternator.


Alternator sounds could be caused by loose bets, bolts, bearings, and brushes, among others. An easy fix for this type of noise is to take out whatever part of the alternator is causing the sound and have it replaced.

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