Last Updated on: 7th September 2023, 12:39 am
Ever heard a knocking, clunking or dinging sound from your car?
It is not always straightforward to determine the source of a knocking sound in a vehicle.
However, it is critical to deal with the noise as soon as you become aware of it, before more damage is caused.
Below are 5 possible causes (and fixes) of that unknown knocking sound.
- Worn suspension components
- Engine knocking
- Damaged engine & gearbox mounts
- Worn pulleys & belts
Above are the most common causes of knocking sounds coming from your car, sometimes they be heard as a rattle or dinging sound.
1. Worn Suspension Components
If you hear a knocking or rattling sound coming from your vehicles wheel arches or from a corner of your car, it’s likely related to your suspension system.
The knocking sound could be caused by any of the following components:
- Drop links
- Anti-roll bar
- Damaged top mounts
- Worn dampers/shock absorbers
Worn Drop Links
Usually a worn drop link (also known as an end link or sway bar link) will sound like a rattling/knocking noise, usually it becomes louder when going around corners or over bumps and uneven surfaces.
You may also notice reduced handling performance, such as more body roll when going around bends and a more twitchy feeling car.
The knocking noise you hear can be due to too much play in the drop links, causing the link or sway bar to hit other suspension or chassis components.
Sometimes, the link may completely snap off, causing the anti-roll bar to freely move around, hitting the chassis and other components.
A broken drop link should be fixed immediately, the car will fail its MOT and is at risk of losing control when driving over bumps or around bends.
Luckily, it’s a pretty simple fix by installing new drop links.
Worn Anti-Roll Bar
The anti-roll bar (also known as a sway bar, anti-sway bar or stabiliser bar) usually does not break but the bushes and joints can become damaged and worn out over time.
When the bushes or joints begin the deteriorate you may notice some clunking and knocking sounds.
Similarly to worn out drop links, you may also notice worsened handling and a louder knocking sound when going around bends or over uneven surfaces or bumps.
Replacing the sway bar is usually easily done at the rear of the car; however, it usually requires the subframe to be dropped down at the front of the car.
This can become expensive, but it needs to be done before you can drive the vehicle again, it will likely fail its MOT and can cause instability and loss of control.
Damaged Top Mounts
A damaged strut or damper top mount can also be a cause of knocking and rattling.
If the top mount completely breaks, the damper or strut will be freely knocking about in the wheel arches, if this happens you must pull over and stop your car immediately.
Other symptoms of damaged top mounts include:
- Reduced handling performance
- Increased stress on shock absorbers
- Wheel alignment issues
- Increased braking distances
- Abnormal tyre wear
You can either replace the top mount or the entire strut assembly.
Worn Dampers / Shock Absorbers
Another reason for a knocking sound could be due to worn shock absorbers (also known as dampers).
Worn shock absorbers are also dangerous to drive with, if you diagnose your car with worn dampers you must avoid driving and get it fixed before driving again.
Other symptoms of worn shock absorbers include the following:
- Excessive weight transfer (body-roll around corners, nose-diving when braking and rear-squatting when accelerating)
- Harsh bouncing and vibration over bumps, especially at higher speeds
- Skipping and traction loss over bumps and uneven surfaces
- A leaking shock absorber
If you continue to drive with a broken damper, you could risk losing control of the car when driving over uneven surfaces or bumps, it also causes a significantly longer braking distance.
Getting a shock absorber replaced isn’t usually a very expensive fix and it’ll fix that annoying knocking sound.
You may also consider fitting coilovers or lowering springs along with new dampers if you’re after improved handling.
2. Engine Knocking
Engine knocking can also be a causing of a knocking, ticking or pinging sound.
There are two main types of engine knocking:
- Detonation & pre-ignition knock
- Rod knock
Detonation & Pre-Ignition Knock
Sometimes, detonation and pre-ignition knock is very subtle and hard to hear and other times it is loud and easy to hear, but it still another cause of a subtle knocking noise.
Below is a video to help you identify what this type of engine knock sounds like.
If the combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, it is referred to as detonation or pre-ignition knock (also known as knocking, spark knock and pinging), depending on the timing of the detonation.
This type of knocking occurs when one or more pockets of air/fuel mixture explode outside of the normal combustion timing in a spark ignition internal combustion engine.
This could become dangerous for the engine and is usually the result of a faulty knock sensor or a bad tune.
It can also occur when switching between fuel types, usually when switching to a lower octane fuel from a higher octane fuel.
Detonation and pre-ignition knock occurs more often in high-performance and tuned turbocharged cars.
Usually, replacing the knock sensors and professionally retuning the ECU can fix this issue. Overall, engine knock such as detonation and pre-ignition could be causing a knocking sound.
Rod knock is a different form of engine knock which is usually the result of worn rod bearings.
The video below shows you what rod knock sounds like.
It can also be accelerated or caused by an incorrect bearing clearance.
The up and down movement of the pistons in the engine causes the crankshaft to spin, which in turn transfers the power to the wheels.
Rod bearings provide for smooth piston movement, but they may get worn out or out of place over time due to the constant movement of the piston.
As the rod bearings wear down, the pistons will begin to rattle against the crankshaft, producing a knocking sound.
In order to fix this type of engine knocking, you may need to replace the rod bearings or have additional work done on the pistons or crankshaft, these components are buried deep inside the engine, making this an expensive and time-consuming repair.
3. Damaged Engine & Gearbox Mounts
Damaged engine and gearbox mounts are another cause of knocking sounds, sometimes you may hear banging or clunking noises instead.
There are other symptoms besides abnormal sounds, such as the following:
- A rocky start
- Increased vibrations
- Jolting when changing gears or accelerating
- Visual wear and tear
One of the signs of damaged engine and gearbox mounts is a rocky start, when starting the engine you may feel and hear the engine/gearbox lurch or rock.
You will likely also notice increased vibrations in the steering wheel, gear selector, clutch and other pedals and your seat.
While changing gears or accelerating you may also notice a jolt. Be sure to check the engine bay for obvious corrosion, cracks or warps on the mounts.
Usually, mounts are made from metal with a hardened rubber insert which deteriorates with time, meaning the older the car the more likely it is you have damaged and worn engine and gearbox mounts.
Below is an image of a worn mount.
4. Worn Pulleys & Belts
Sometimes a worn or damaged pulley or belt can cause a knocking sound, it can also sound like a squeaking, chirping or slapping sound.
There are two main belts in a car, as shown below:
- Timing belt
- Serpentine/auxiliary belt
Certain cars may have three belts, but usually there are two.
The knocking sound may also be due to worn or damaged pulleys hitting other components, they may warp, bend or break.
You can check a belt for wear and tear by visualising inspecting it, if there is cracks, fraying or glazing to the belt then it is worn and needs replacing, the belts may also be loose due to a broken or worn belt tensioner.
Usually, the fix requires changing the belts and pulleys if they are damaged.
Misfiring can also cause a similar sound or feeling to knocking.
Technically speaking, a misfire occurs as a consequence of insufficient (or no) combustion occurring in one or more of an engine’s cylinders.
A misfire will often manifest itself as hesitancy or shaking while the vehicle is accelerating or in motion.
Therefore, you can usually fix a misfire by replacing the spark plugs or ignition coils.
If you feel or hear a knocking in your car, something has likely gone wrong, broken or worn out.
Unless it is an interior rattle, you should get the vehicle checked professionally and avoid driving.
Continuing to drive with a knocking sound may cause damage to the car and if it is related to suspension system you could even lose control of the vehicle.
The most likely reasons for knocking is due to worn out suspension components.