Car Makes Grinding Noise When Idle & Driving Slow? (6 Reasons)

It’s always nerve-racking when your car makes funny noises you aren’t supposed to hear. Grinding noises when your vehicle is idle and slow movement can mean serious issues.

We’ll help you pinpoint the problem by explaining the top reasons you might be experiencing these two problems together.

First, check this article if your car won’t start at all while making a grinding noise.

1. Your Alternator Has a Bad Pulley or Bearings

Your car’s alternator plays a massive role in the operation of your car. It’s one of the primary power sources in the vehicle. One of its main duties is to charge your battery so that it always stays strong enough to start your car.

However, its more important task is to provide a consistent power source for all of your accessories. Alternator pulleys and bearings tend to wear over time.

A loud grinding sound can occur if the pulley becomes loose enough to move around on the belt that drives all your accessories.

The grinding noise you notice could be from objects touching each other or from the belt losing its tension.

However, the problem may not be coming from the alternator’s pulley at all. It can also have worn bearings, loose bolts, a damaged rotor, or something else. These alternator problems are likely to cause undesirable sounds when your car is running.

Examples of the sounds a bad alternator makes are grinding, whining, squealing, and clunking.

These issues may also cause your car to run slowly because of the loss of power in the accessories.

A defective alternator will not charge your battery at all, and your car will rely on only the battery’s strength to operate its accessories. This problem could cause your vehicle to run slowly and eventually not start.

How To Know if It’s Your Alternator

Alternators can fail with no visual symptoms at all, but there are times when you can clearly tell that they’re the culprit.

Also, it’s NOT your alternator if you have an electric car. Electric vehicles don’t have alternators.

Here’s what you can do to check:

Look for Uneven Belt Movement

The first thing to do if you hear grinding noises coming from your car while at idle is to open the hood and see if you notice odd movements in the accessory belt. Your serpentine belt will most likely be visible on the left side of the engine, depending on how your motor is oriented.

It’s a long belt that looks to be wrapped around many round pulleys. Each pulley goes to an important vehicle component. Thus, anything that sets off the perfect flow of the belt causes noises and catastrophic performance issues.

You might notice odd movements as the belt rotates, which is a tell-tale sign of an alternator issue.

Check Also: Car won’t keep running idle.

#1 Listen Closely

You can listen to the noise with your ear or a mechanic’s stethoscope. Because noises can occur in different places and sound like they’re coming from somewhere else, you may want to invest in a good stethoscope to find the correct cause.

Move your stethoscope around to see if you can confine the area where the noise originates. You’ll hear it coming from the alternator if it’s the offending component.

#2 Check Visible Bolts

Sometimes a problem is as simple as a loose bolt that you can tighten on your own.

We advise you to look under your hood, locate the alternator, and check the visible bolts to see if any of them might have lost some of their tightness.

In that case, tightening them with a tool may resolve your issue.

#3 Have Your Alternator Tested

You can test your alternator with a voltmeter or multimeter to see if it has internal problems. Your reading should not be any lower than 12 volts.

Less than 12 volts indicates that you need an alternator replacement.

#4 Other Signs of Alternator Issues

A bad alternator will usually cause your battery light to illuminate at some point.

The light lets you know that your charging system and battery do not have the appropriate amount of energy to run your vehicle effectively. You can expect the car to cease running or start shortly after you see that light.

You may also see your check engine light.

Flickering headlights are wonky accessories are another sign of a bad alternator.

At some point, you may notice that several lights flicker on and off when there aren’t any issues with those components.

We also have an article to help you find the problem if the car makes a grinding noise while accelerating or braking.

2. Your Serpentine Belt Is Worn

Your Serpentine belt wraps around all the pulleys connected to various items such as:

  • the crankshaft,
  • water pump,
  • power steering,
  • alternator,
  • idlers,
  • etc.

You will likely hear grinding noises and experience poor performance if your belt is loose, worn, or damaged.

This issue must be resolved quickly, or your car will stop running when the belt finally gives way. In most cases, a visible inspection will uncover a worn serpentine belt.

Watching the belt move while you idle should also produce some visible signs.

RELATED: Serpentine Belt Problems? 7 Problems & Solutions

3. You Have Transmission Problems

A transmission issue can cause your car to make grinding noises and go slow.

The lack of fluid, for example, causes your transmission to operate without lubrication, which means that metal components touch each other dry.

Low fluid might be the reason for the grinding noises, and a failing transmission can cause your vehicle to move slowly and refuse to shift.

The first thing you need to do is check your vehicle’s transmission fluid level. You will find a dipstick under the hood if your car has one.

You must check the dipstick while the vehicle is running and inspect it to see where the level is.

You have just discovered your issue if you notice the low transmission fluid level. Check your owner’s manual for the correct fluid and refill it ASAP.

You can also check for transmission problems by putting your car into different gears at idle and listening to see if the grinding noise gets worse when you switch gears.

This occurrence indicates that your transmission has an internal issue you must address immediately.

4. Your Engine Bearings Are Failing

Worn engine bearings can cause a great deal of noise in your car, and their lack of effectiveness can cause the vehicle to operate slowly.

These bearings exist at the lower end of your motor, and they’re in place to prevent metal-to-metal contact and friction.

Contamination, lack of lubrication, and excessive wear can cause them to break down. Once they wear down, you can hear the noise from the rubbing parts, and your vehicle will most likely run slowly or have other performance-related issues.

You may also notice reduced oil pressure, metal pieces in your oil, or other noises, such as knocking.

5. You Have Worn Brakes

Your braking system can also make a lot of noise if it lacks lubrication or has worn to a serious extent. Most brake noises occur when trying to slow your vehicle down.

You’ll hear grinding noises if your brake pads have worn down to the metal-touching-metal stage.

You’ll likely hear similar noises if you have bad rotors or calipers.

Brake problems usually don’t cause vehicles to slow down, however. 

Thus, the problem is most likely not your brakes if you are experiencing a power loss with the grinding noises. Still, you can have a mechanic look at your brakes to check for problems.

6. Worn Motor Mounts

Your motor mounts can cause you to hear grinding noises in your vehicle.

They hold your engine intact but can wear over time. When that happens, the weight of the motor can cause stress on your serpentine belt or put pressure on other components and cause a grinding sound.

You will notice a broken motor mount if you look under your hood while the car is running and see a lot of play in the engine movement. 

Broken motor mounts are likely to cause you to have performance issues and bog you down because of the weight of the shifting engine.

Now you know some of the most common causes of grinding noises.

The list is not conclusive, however, and it would be wise for you to visit a trustworthy mechanic if you cannot pinpoint the issue. Your car’s life depends on you having the problem diagnosed and treated.


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