Knocking Noise on Passenger Side of Car: What Are the Reasons? (2023)

There's nothing more worrying than a strange noise from your car. Sometimes these noises come from specific parts of the car, or they might seem hard to pinpoint. One common type of noise is a knocking noise from the passenger side of your car. What could this sound mean, and what are the reasons you're hearing it?

A knocking noise from the passenger side of the car usually implies that something has gone wrong in the front of the car. There are many different potential causes, but common issues are problems with some parts of the suspension, the engine, or the fan blower. Figuring out the cause of the problem will require observing when the noise comes up, as well as any other symptoms that might be present in your car.

In this article, we'll discuss the different causes of a knocking noise from the front of your car, as well as what needs to be done to fix it.

Knocking Noise on Passenger Side of Car: What Are the Reasons? (1)

What Causes a Knocking Noise from the Passenger Side of the Car?

There are many different potential causes of a knocking noise from the passenger side of the car. Usually, this means that there's some problem with the car that requires attention. Understanding and finding the cause of the knocking noise in your car is important because it could indicate a minor problem that will become worse with time.

A knocking noise from the car could be the result of a problem with the car's suspension, an engine problem, or a faulty actuator in the dashboard.

We'll take a look at each of these different causes, and talk about what the problem means for your car.

1) Faulty Blend Door Actuator

One of the most common causes of a knocking noise from the passenger side of the car is a faulty blend door actuator. If the sound seems to be coming from inside the dashboard, then it is almost certainly a faulty or failing actuator.

The actuator controls a small flap called the blend door, which is responsible for opening and closing the flow of hot and cold air into the cabin. When the actuator fails, it will have trouble turning the blend door. This results in a repetitive knocking noise from inside the dashboard.

Apart from a knocking or clunking noise from the dashboard, another symptom of a failing actuator is when the AC can't produce the correct temperature. If the AC blows too hot or too cold, then the blend door is probably stuck.

A bad blend door actuator is not a serious or urgent problem, and it can be ignored if you're willing to live with the knocking noise and malfunctioning AC. If not, you can get a replacement online, and replace it yourself or have a mechanic do it for you.

2) Suspension Problem

A common cause of a knocking noise from the passenger side of the car is a problem with the vehicle's suspension system. The suspension system is responsible for maintaining the stability of the car and supporting the vehicle's weight on the wheels.

Many parts of the suspension system are under compression. As a result, when there is a problem with the suspension, it can cause knocking sounds. This is especially common when going over bumps or rough terrain.

Different parts of the suspension could be damaged or affected. The most common culprit is the struts. The knocking noise could be caused by a leaking strut on the passenger side.

Whatever the cause of the knocking noise is in the suspension, the system is complicated to work on. If you suspect the problem is from your car's suspension, it is important to have it inspected by a professional mechanic. The mechanic will be able to diagnose and repair the issue.

3) Wheel Bearings

Another common culprit when it comes to a knocking noise from your car is a problem with the car's wheel bearings. Bearings are a very important part of your car that support the wheels and allow them to rotate smoothly on the axle.

Over time, wheel bearings can wear out, as a result of poor lubrication, dirt, or age. When will bearings wear out, the wheel won't be able to turn freely on its axle. Apart from reduced acceleration, and a dragging feeling from the tire, worn wheel bearings can produce a wide range of funny sounds.

Worn wheel bearings can produce growling sounds, whining or chirping sounds, or knocking noises. One solid sign that you have a worn wheel bearing is that the sound gets louder as the car accelerates.

Worn or damaged wheel bearings will need to be replaced with new ones. By the time wheel bearings have worn down to the point that they are producing a knocking noise, there is a high chance that there is damage to the ball joints of the wheel. It is recommended that you have the ball joint inspected when the wheel bearing is being replaced.

4) Failed Motor Mounts

Motor mounts secure the engine and the transmission to the car's frame. They are built to absorb the vibrations of the engine which prevents the engine from shaking the frame of the car. Without motor mounts, modern vehicles would not ride so smoothly.

When the motor mounts fail, you're likely to hear a knocking sound from the engine. This is because the engine isn't being held in place, and is shaking and vibrating around in the engine compartment. You're also likely to notice that the car vibrates and shakes more than normal when the engine is running.

As you can probably tell, this isn't safe. The vibration of the car could result in the driver losing control of the steering wheel. Also, when the engine is shaking around inside the engine compartment, There's a high chance that the vibrations could cause something to come loose or wear down inside the engine, leading to further complications.

A damaged motor mount will need to be replaced. Fortunately, new motor mounts are generally very cheap. An engine has more than one motor mount, so you will need to identify which ones are damaged to know how many you need.

5) Damaged Rotor or Brakes

In some cases, a knocking noise on the passenger side of the car can be caused by a problem with the brakes. If the brake rotor wears down or rusts, it can cause a knocking sound when the brakes are applied and the brake pads come in contact with the rotor.

A knocking noise can also be caused by loose or damaged brake calipers.

If you suspect a problem with your car's brakes, you should stop driving as soon as you can, and inspect the brakes on the passenger side of the car. Check for signs of corrosion on the brake rotor. You should also check to see if there are signs of damage on the calipers.

Damaged brakes are a serious issue that should be addressed as soon as possible. You should have your car checked by a mechanic as soon as possible. The damaged parts of your brakes will need to be replaced with new ones.

6) Engine Problems

Generally, knocking noises from the engine will distinctly sound like they are coming from the front of the car, rather than the passenger side. However, in some cases, a knocking noise on the passenger side of the car can be caused by a problem with the engine.

There are many different engine problems that can result in a knocking sound.

  • Faulty drive belt
  • Faulty tensioner
  • Lean fuel mixture
  • Wrong grade or type of fuel
  • Bad knock sensor
  • Worn rod bearings

If you suspect an engine issue, you should get your car to a mechanic immediately. Ignoring a knocking noise from the engine could result in further damage and costly repairs.

7) Bad Exhaust System

Finally, another cause of knocking from the passenger side of the car could be an issue with the car's exhaust system. The exhaust system runs from the engine, under the car, and to the exhaust pipes at the rear of the car. If part of the exhaust system rusts or becomes loose, it could result in a knocking sound from under the car. This knocking sound might become more evident when the car picks up speed or passes over bumps.

A damaged exhaust system could leak, which will cause the car to emit harmful emissions into the atmosphere. This is dangerous for the environment and the driver, so if you suspect an issue with your exhaust system, you should have it inspected and repaired by a professional mechanic as soon as possible. Ignoring exhaust problems could be detrimental to your health if harmful fumes begin to enter the cabin.


A knocking noise from the passenger side could have a range of different causes. You might need to have your suspension, engine, or air conditioning checked.

Ignoring a knocking noise from your car isn't a wise decision, as it could be caused by serious problems that might even pose a risk to your safety, such as exhaust problems or brake problems. If you hear a knocking noise from your car, have it inspected by a professional mechanic as soon as possible.

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