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Do you hear a grinding or scraping noise coming from your car’s undercarriage while driving? Not only is the sound annoying, but it can also indicate a problem that compromises overall vehicle safety. You’ll want to find out what’s causing the noise so that you can fix the issue right away.

What Causes a Grinding Noise When Driving? 4 Common Causes

Unfortunately, there isn’t a one-size-fits-all answer as to why you might be hearing a grinding noise from your car’s undercarriage while driving. To determine the root cause of the concern, you (or your mechanic) will need to do some troubleshooting.

Once you start to dig in, there’s a good chance you’ll find the noise coming from one of the following sources.

Worn Brake Pads or Shoes

Brake pads and shoes help create the friction needed to bring your car to a stop. In a disc brake system, the pads are pressed against a disc-shaped rotor to halt the vehicle. When a drum brake system is used, shoes are pushed outward against a circular drum to create the same effect.

asbestos brake pad with blurred disc brake in background
Brakes that are worn down to the backing plates can produce a grinding noise when driving.

Severely worn brake pads or shoes can create a grinding noise while driving. The problem happens when the brakes are worn down to the backing plates (or wear indicators), allowing for constant contact with the drum or rotor.

Rusted Rotors

When a vehicle sits for an extended period, the surface of the rotors will accumulate rust. The rust can cause the brakes to make a grinding noise whenever the car is in motion. Usually, the noise goes away quickly, as the rust gets cleared off by the brake pads each time the brakes are applied.

Bent Backing Plate

Drum and disc brake systems both use backing plates. The backing plates are located behind the brakes to shield the braking components from water and debris. In a drum brake system, each backing plate also provides a mounting point for the brake shoes and related components.

Because backing plates are made of thin metal, they can easily get bent. When that happens, the backing plate then contacts the rotor (in a disc brake system), creating a grinding noise. It’s also possible for the backing plate to contact the drum in a drum brake system, though the issue is far less common.

Bad Wheel Bearing

Your car has a wheel bearing (or axle bearing) at each wheel. Each wheel bearing allows one of the wheels to rotate with minimal friction. The wheel bearings also help support the weight of the vehicle.

When a wheel bearing starts to go bad, it often makes a growling or humming noise when the vehicle is in motion. If the faulty bearing is left unchecked, it will usually begin to make a grinding sound.

You’ll notice that the frequency of the sound corresponds to the rotation of the tires. Also, the sound will increase with vehicle speed (though it may go away at a certain point) and may get louder when turning in one direction or the other.

FAQ

Is it safe to drive with a grinding noise?

A grinding noise can indicate a safety concern, such as worn-out brakes or a bad wheel bearing. As such, you’ll want to address the problem right away to ensure your vehicle remains safe and dependable.

How do I fix a grinding noise when driving?

Because a variety of problems can cause a grinding noise while driving, you (or your mechanic) will need to do some troubleshooting to get to the bottom of the problem.

Brake Chatter or Roughness Assessment
Because a variety of problems can cause a grinding noise while driving, you will need to do some troubleshooting to get to the bottom of the problem.

Below, you’ll find a few steps that you can take to help diagnose the concern. If you’re unsure of where the noise is coming from, you might need to repeat each step at all four corners of the vehicle.

  1. Perform a visual inspection: The first step is to safely raise and support the vehicle, remove the wheel/tire assembly, then perform a visual inspection. You’ll want to look for signs of the backing plate contacting the rotor, rusted rotors, and other obvious issues.
  1. Check the brake pads or shoes: Next, remove the caliper or drum to inspect the brake pads or shoes. Be on the lookout for brakes that are worn down to the backing plate or wear indicator. You’ll also want to check for friction material that’s crumbling or flaking off, which can also be the source of a grinding noise.
  1. Inspect the wheel bearings: The final step is to inspect the wheel bearings. You can learn more about wheel bearing diagnosis by reading this article.

Once you find the cause of the noise, you can perform the necessary repairs to fix the problem.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

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Comments

  1. Peter Cochetti says

    do you have a guide on how to replace 2010 mazda 3s rear rotors and pads?

    I have done mechanic work before but it was drum brakes and the wheel cylinder honing, etc.
    Would these be easier to replace.

    I am retired and do not need the car much, so it could be down for a while if needed.

    What would be the hardest part (getting old rotors off?) do you still need to bleed the brakes afterword?

    • Hello Peter,

      Replacing disc brake pads is usually much easier than replacing drum brake shoes. However, on your vehicle, you will need a special tool to turn the caliper piston back in its bore before installing the new pads. There is no need to bleed the brakes as long as you do not disconnect the brake lines or allow air to enter the brake system in any other way.

      We do not have a guide for replacing the pads and rotors on your vehicle. You might be able to find something helpful on YouTub. If not, we suggest consulting a repair manual or repair database, as outlined in this article: https://www.carparts.com/blog/why-you-should-always-consult-a-repair-manual/

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