Your Handbook Lists the Car Noises to Ignore and One to Act On

Ford, Kia, Volvo and Polestar print short lists of car noises they call normal: an occasional brake squeal, a cooling fan that runs on after switch-off, a click from a diesel filter cleaning itself, the sounds of a hybrid. Ford’s and Kia’s pages also name the squeal that is a warning, and the MOT manual tests very little by ear. Ford’s line between the two readings is occasional against continuous.

Key takeaways:

• Ford and Kia handbooks call some brake squeal normal, and the same pages describe a squeal that can mean worn pads.
• Ford, Volvo and Kia list fans, filter clicks and hybrid sounds as normal, and the MOT manual tests very little by ear.
• A maker’s list is short and comes with its own hedge, so a noise that is not on it is a question for a garage.

What the Handbooks Call Normal

Brake Squeal and Groan in Ford and Kia Handbooks

Ford’s 2012 Focus handbook says: “Occasional brake noise is normal and often does not indicate a concern.” The page adds that the brakes can give an occasional or intermittent squeal or groan when applied, and names environmental conditions such as cold, heat, moisture, road dust, salt or mud as the usual cause. Ford’s 2019 Fiesta handbook opens its brake note with a shorter version of that sentence.

Kia’s 2022 UK handbook puts it in similar terms. Under a “certain driving or weather condition” a car can squeal or make other noises, and the page states: “This is not a brake malfunction but a normal phenomenon.” Roads treated with de-icing chemicals can bring brake noise too, and Kia tells drivers to apply the brakes where traffic allows, to clear the chemicals.

Kia adds that cars fitted with its large-diameter Brembo performance brakes can screech, crack and scratch, and calls that normal too. Each statement covers a named handbook and a stated condition, not every car or maker, and makers revise the pages. A cold-morning squeal that fades as the brakes warm sits inside Ford’s list of causes. The handbooks give no such cover to a noise that stays.

Fans After Switch-Off and Clicks From a Diesel Filter

Volvo’s UK support page for the XC60, updated in October 2024, states: “It is normal for the engine’s cooling fan to keep running a while after turning the car off.” Ford’s 2012 Focus handbook says: “After you have switched your engine off the fans may continue to run for a short period of time.” Neither maker gives a figure in minutes.

Ford’s diesel particulate filter section holds a second sound. Ford’s 2019 Fiesta handbook says that at low speed or idle, while the filter cleans itself, a hot metallic smell and a clicking metallic sound can appear. Ford blames the high temperatures reached and calls it normal. The 2012 Focus handbook says the same. Both are diesel filter texts and carry no claim about petrol cars.

The Fiesta text adds that cleaning comes round every 100 to 310 miles and lasts 10 to 20 minutes, that the interval varies with driving style, outside temperature and altitude, and that the engine or exhaust sound can change meanwhile. A filter that cannot finish cleaning can end in a dashboard warning, and what a DPF warning light means is soot build-up the filter has not cleared.

What Hybrids and Electric Cars Add

Kia’s 2024 UK hybrid handbook says hybrids sound different from petrol cars. Owners can hear the battery system behind the rear seat, the regenerative brakes when the pedal is applied, and the engine compartment as the system switches on or off. A motor sound there is normal with the pedal pressed or released and the system off, or when the driver’s door opens. The page concludes: “None of these sounds indicate a problem.”

Both makers add sound on purpose. Kia’s Virtual Engine Sound System plays an engine sound at low speed so pedestrians can hear the car. Polestar’s UK manual for the Polestar 3 lists, among other sounds, an artificial low-speed sound, a reversing sound, climate system noise at high power and a quiet mechanical sound as the parking brake engages, and says: “Some are simply mechanical sounds, which are normal and nothing to worry about.”

Polestar adds its own hedge: “It’s not a complete list of all sounds that you may hear and is not meant to be used to diagnose issues with your car.” KYB, a suspension maker, says worn mounting bearings knock, and that owners notice it even more in hybrid and electric cars, which KYB puts down to the quietness of the engine. A quiet cabin exposes mechanical noise.

The Same Noise With a Different Meaning

The Brake Squeal That Is a Warning

The Kia page that calls squeal a normal phenomenon describes a second squeal. When pads are worn, a high-pitched warning sound comes from the front or rear brakes, and Kia says: “You may hear this sound come and go or it may occur whenever you depress the brake pedal.” The page continues: “This brake wear warning sound means your vehicle needs service.”

Ford’s 2019 Fiesta note draws its line in the same place. After calling occasional brake noise normal, it says a metal-to-metal sound, continuous grinding or a continuous squeal could mean worn-out linings. The current MOT inspection manual says some pads carry a metal wear indicator that squeals against the disc once the pad is excessively worn, and adds: “An illuminated brake wear indicator is not a reason for failure.”

Side by side, the two makers draw the line in different places. Kia ties the normal squeal to a “certain driving or weather condition” and the warning sound to coming and going, or sounding whenever the pedal is pressed. Ford sets occasional against continuous. Neither gives a further test, so a squeal that persists belongs with a garage. Left alone it gives way to grinding, and what grinding brakes mean is pads worn through and a damaged disc.

A Knock Over Bumps Is Usually Not the Shock

A knock that shows up over speed bumps and potholes and goes quiet on a smooth road usually points to a worn drop link or bush in the anti-roll bar rather than the shock absorbers. The sound alone does not name the part, and KYB and the MOT manual each point to a different place to look.

KYB, a suspension maker, names another candidate. In a March 2023 workshop article it says worn bearings in a suspension mount create knocking noises, and its guideline is that worn struts probably mean worn mounts. A mount is one part among several that a garage checks, and the diagnosis is a garage job, not a guess from the driver’s seat.

The MOT manual looks for wear, not a knock. The tester checks play in spring pins and bushes with a small pinch bar or wheel play detectors, rejects an excessively worn shock absorber bush or a shock absorber with negligible damping, and rejects a MacPherson strut top bush only when play comes from wear or maladjustment. The manual asks the tester to measure play, not to judge a noise.

A Hum That Rises With Road Speed

A hum or growl that rises with road speed and changes as the car is steered is most often a worn wheel bearing. Tyres, a CV joint and a gearbox can produce something similar, so the sound alone settles nothing. The difference lies in when the sound changes, not in how loud it gets.

This is where the MOT inspection manual tells the tester to listen at the wheel. With each wheel raised clear of the ground, the tester spins it and listens for roughness in the bearings. A bearing that is excessively rough is a Major defect, and one likely to collapse is Dangerous. Play is measured separately, by rocking the wheel or with wheel play detectors.

Major and Dangerous are MOT defect categories, and both fail the test. The two checks, play and roughness, settle a suspect bearing for a tester in under a minute. A hum on the road is a reason to have a garage lift the car and run them. The sound narrows the search, and only a raised wheel settles it.

What an MOT Tester Listens For

Exhaust Noise Is Left to the Tester’s Judgement

The MOT inspection manual tells the tester to use judgement on exhaust noise. The assessment comes in the emissions test or, on cars not subject to one, with the engine revved to around 2,500rpm, or half the maximum engine speed if that is lower. The tester inspects the silencers and listens to the result.

The yardstick is a comparison: exhaust noise must not sit unreasonably above that of a comparable car with a standard silencer fitted and in average condition. Noise over what is permitted is a Major defect. The nuisance section of the manual gives no decibel figure, so a loud exhaust is the tester’s judgement against that benchmark.

A loose silencer can rattle, and the manual has a separate entry for it. Any part of the noise suppression system that is insecure is Major, and any part likely to become detached is Dangerous. Both fail the test. A loose part and a loud exhaust are separate defects with separate entries, and the tester can record either one.

Engine Noise the Tester Will Not Test Through

Section 8.2 of the MOT inspection manual lists the cases where the diesel smoke test should not be carried out: too little oil in the engine, oil pressure too low, abnormal engine noise, a tampered governor, or a camshaft belt in unsatisfactory condition. A tester who judges the test unsafe must record the reason for refusing on the VT30.

So abnormal engine noise can stop a diesel test being carried out at all. The manual treats it as a reason to halt, and the tester writes down why. A tester who hears it can decline the smoke test, and a driver who hears the same noise has a reason to ask a garage to look before the next MOT.

The camshaft belt sits on that list too. The one audible warning of a failing belt is a noise from the timing cover end of the engine, and it usually comes from a tensioner or an idler pulley rather than the belt, which is the one audible cam belt warning in the site’s own research.

When the Noise Needs Proving

When the Dealer Says It Is Normal

The Motor Ombudsman receives complaints about noise at idle, in acceleration, at a cruise, in turns, under braking and after the engine is turned off. It says a noise is not always the symptom of a fault, and that manufacturers often set tolerance levels for how much noise a characteristic should make. Its page is written for a new car.

If the owner disagrees with the manufacturer, the Ombudsman recommends a second opinion from another main dealer or an engineer. Under warranty rights, the owner tells the manufacturer of that intention first, so that the cost of a successful report can be claimed back. Under legal rights, the owner follows the process in the Consumer Rights Act and lets the seller try to diagnose the noise.

If the seller finds no fault, the Ombudsman says to tell the seller of the plan to get a second opinion, which lets the owner recoup its cost from the seller. A handbook is the document a maker is likely to point to, so its normal list is worth reading before a noise reaches a dealer. That is an inference from the Ombudsman’s tolerance wording, not a rule it states.

Making a Noise Easy to Find

KYB’s workshop guide to diagnosing worn suspension mounts shows how to keep a test repeatable. The maker describes a quiet road near the workshop that can be used again and again: about a mile, about three minutes, no more than about 30 mph, with a speed bump, a place to brake and accelerate, and steering checks. The procedure is written for mechanics, and a garage can run it.

A driver can borrow the method without the route. Note when the noise happens: pulling away, braking, turning, over bumps or at a steady speed. Note whether it follows road speed or engine speed, and whether it happens every time. KYB’s workshop then rules out other parts, such as ball joints and bushes, before blaming one.

Hand the garage those notes and the noise can be repeated rather than hunted. A noise that comes only on starting is a separate diagnosis, and what each starting sound tells you belongs to that one.

A handbook’s normal list is short, written for the maker’s own model, and sits on the same page as the squeal that is a warning. The MOT manual leaves most noises to the garage: its few checks cover an exhaust, a wheel bearing spun for roughness and an engine too noisy for a smoke test. The noise a handbook names, under the condition it names, is the one to leave alone. Every other noise is a question for a garage.

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Reviewed by Preetam Gadekar