Knocking Noise Under My Car When Driving

A loud ticking, clunking, grinding, banging, squealing, or knocking sound under your car can signal an underlying problem that you need to address immediately.

If the knocking sound is coming from the front wheels, but you’re not sure what could be causing it, this post will list several reasons to help diagnose and fix the problem.

When driving, several factors can cause knocking noise under your car, including misaligned tires, bad ball joints, axle problems, loose lug nuts, faulty knock sensor, old spark plugs, worn brake pads, and bad shock absorbers.

What is a knocking sound under the car?

Any unfamiliar sound in your car serves as an alarm signal and a reason to pay attention to your car’s technical condition. A knocking sound is a backlash appearing from the natural wear and tear of car parts and other technical errors. The noise mainly comes from rubbing parts or elements.

If your car is making louder noises and you’re not sure where they’re coming from, you could be dealing with an engine knock, often referred to as pre-detonation or pre-ignition.

This uncontrolled combustion process occurs because of extreme temperatures or pressures in the combustion chamber. As the piston compresses the air-fuel mixture, this mixture heats up. 

Other factors that cause more pressure than the fuel can handle and lead to ignition before the spark plug fires include; poor fuel quality, aggressive timing, and incorrect octane.

Common causes of knocking noise under your car when driving

Here are the common reasons why your car might be producing a knocking sound every time you drive.

Too low octane

Each engine comes with a specific number of octane levels. The octane number determines fuel tolerance. Generally, the higher the octane number, the farther the piston is likely to move toward the spark plug, resulting in greater power output.

To reach its maximum travel level, it makes multiple pockets of the air-fuel mixture if the octane number is low. As a result, the vehicle will produce a knocking sound and decrease its performance.

Bad ball joints

Some ball joints connect the car’s wheels to the suspension system. Ball joints help give the wheel’s proper range of motion, allowing you to turn right and left smoothly whenever you turn the steering wheel.

When they begin to wear out, you will hear a grinding or knocking sound every time you adjust the steering wheel. The noise will be more prominent when you make a complete turn on either side.

Worn wheel bearings

The wheel bearing helps your tires to spin freely when the vehicle is in motion. If the bearings become too dirty or begin to seize up, they might not function properly, and the result is a knocking sound when you’re driving. In the worst cases, the wheels may lock up and fail to move completely.

Misaligned tires

Misaligned tires occur due to wear and tear or when you drive over obstacles such as hard, big rocks, or potholes. If your tires are not well-aligned or there is some form of damage in one of the tires, you will experience a clunking noise or a knocking sound. If the tires are in good condition, proper alignment can help eliminate this problem.

Loose lug nuts

Lug nuts connect the steering wheel and the tires for coordination. That means you need to remove them when changing a flat tire. If you hear a knocking sound after switching tires, either because it was flat or you had your tires rotated, the problem could be the lug nuts.

The only explanation would be that they were not correctly retightened.

Problem with brake pads

When you have worn out brake pads, you might not experience any noise when accelerating, but when you’re braking. If you’re not sure when was the last time you changed your brake pads, it may be the right time to get your mechanic to check them and replace them.

Never drive a car with braking problems, as brake failure can lead to a crash.

Bad shock absorbers

Shock absorbers hardly produce any sounds unless you’re driving on an uneven road. These could be in the form of knocks and squeaks. To check if your shock absorbers are bad, press hard on the trunk and fenders and listen.

It’s not safe to drive a car with faulty shock absorbers as the braking distance increases when you hit the brakes suddenly.

Worn knock sensor

Manufacturers today equip modern vehicles with an engine knock sensor that detects and communicates to the ECU to diagnose problems. If the knock sensor is faulty, it can send incorrect signals to the ECU. When this happens, the computer will malfunction and use fuel with an air-fuel mixture proportion higher than required, resulting in a knocking sound.

Old spark plugs

Spark plugs are critical components for the combustion of air-fuel mixture to produce adequate power for the engine to function efficiently. Spark plugs can wear out over time, resulting in delayed and reduced spark.

This causes the engine to make a knocking noise during acceleration. Using the wrong spark plugs can also cause knocking sounds as they may not tolerate the engine’s heat and therefore won’t work correctly.

Knocking sound when starting the car

The most common reason for a knocking sound when starting your car is a problem with the starter or the transmission’s flexplate. The situation can quickly escalate if not addressed immediately, and it’s not cheap. You might want to get your mechanic to check the problem and fix it before driving the car again.

What causes clunking noises when braking?

If you notice a clunking noise when braking or decelerating, you might have a problem with your brake pads, loose wheel bearings, or worn-out ball joints. These problems put you at serious risk of an accident or injury, as they’re a clear indication that there is a problem either with the wheels or the brakes.

You may need some new brake pads or a completely revamped steering system and suspension to fix the problem.

Random noise at high speeds

If you experience knocking, rattling sounds when driving on the highway, something in your vehicle could be loose or incorrectly fixed. It can be a  loose part like the trim,  bumper, or even lug nuts. To fix the problem faster without incurring too much cost, you need to figure out exactly what part of the car the sound is coming from and when it’s happening.

If it is under the car, check everything from the wheels to the engine. If the sound only happens at a certain speed, you’re probably dealing with a problem in the internal system.

Knocking sound when accelerating

Knocking noises that occur only when you accelerate signal a problem with the engine.  In most cases, the engine could be straining every time you accelerate, either from a piston slap or low oil pressure. Let your mechanic check the engine to determine the cause and fix it before it gets worse.

Knocking sound when driving on bumpy roads

Squealing or knocking sounds when driving on bumpy roads signals a suspension issue. You can get to the nearest mechanic to inspect the suspension, control arms, or stabilizer links to know where the sound is coming from before the noise becomes an accident.


Can I still drive a car with knocking sounds?

If you start your car and hear knocking noises, don’t drive. Instead, check if it is igniting correctly. This could be due to low fuel or spark plugs. If the sounds start when you are on the road, find a safe place to stop depending on the noise level and find help.

How much does it cost to fix the knocking sound?

Fixing sounds under the car generally costs between $80 to $5000 depending on the problem, type of car, and labor required. In most cases, it involves buying and replacing parts like brake parts and spark plugs.

Do wheels cause a knocking noise?

No. The tire itself cannot make odd sounds if it is in excellent condition. However, the parts responsible can produce knocking sounds if they are not properly aligned, replaced, or rotated when needed.