Most cars make some noise. A good rule is that any sound that changes with speed, steering, braking or temperature is worth paying attention to; the ones that stay steady in the background are usually fine. Below is a plain list of the noises drivers most often ask about, what they tend to be, and which ones mean pulling over.
Ticking from the top of the engine
A rhythmic tick that rises and falls with the revs is often the valvetrain. On an older engine it can simply mean the oil is low or past its change interval. Check the dipstick when the engine is cool, top up if it is below the minimum, and get it serviced if the ticking does not go quiet after a gentle drive.
A sharper, more metallic tap that stays after a warm-up may be a hydraulic lifter or a tappet; it wants a garage, but it is not usually an emergency.
Whining that changes with speed
A rising whine that climbs with road speed and drops again when you coast is a wheel bearing in most cases, especially if it changes pitch when you weave gently on an empty road. The front of the car is the most common place, and it tends to get louder with mileage. It is not a stop-the-car problem, but a failed bearing can seize, so book it.
A whine that tracks engine speed, not road speed, is different. On a manual, listen in neutral: if it goes quiet with the clutch in, the input shaft bearing is tired. On an auto, a steady whine at idle can be the transmission pump.
Squealing on start-up or when you steer
A loud, almost birdlike squeal when you start a cold car and fades after a few seconds is the auxiliary belt (the one driving the alternator and other accessories) slipping on a pulley. Belts stretch; tensioners wear. A garage can inspect it in minutes. If the squeal comes back every time you turn the wheel hard, the belt has had it.
Grinding when you brake
A light, dry squeal from the brakes when they are cold on a damp morning is normal and goes away after a stop or two; many modern pads have a wear indicator that deliberately squeaks. A rough grinding that you can feel in the pedal is different: the pads are metal-on-metal against the disc. The disc is being destroyed while you drive.
Stop drivingIf the pedal feels soft or sinks slowly to the floor, or you hear real grinding on braking, stop driving the car and call a garage. Brakes can fail progressively, then suddenly.
Hissing under the bonnet
A gentle hiss after you switch off is usually the engine cooling; fluid moving in the system, metal contracting. A louder hiss with the engine running, especially one you can locate to a vacuum pipe or an EGR hose, points at a split pipe. The engine may run roughly at idle. It is not an emergency, but expect a check engine light and a drop in fuel economy.
A hiss combined with a sweet smell and steam from the vents is coolant: a leaking hose, a split expansion tank, or a head gasket starting to go. Do not keep driving it hot; see below.
Knocking from underneath
A single, dull knock every time you go over a bump or pull away is usually a worn anti-roll bar link or a drop link at the front. A repeating clonk when you turn tight on full lock, like an old-fashioned typewriter, is a classic sign of a failing CV joint on a front-wheel-drive car. Neither is an immediate stop, but both earn a trip to a garage.
Roaring that gets louder as you speed up
A steady, deep roar that comes in around 40 mph and gets louder as you push on is a tyre problem more often than a mechanical one; a cupped or scalloped tread pattern, or a tyre with a damaged belt inside. Swap the fronts and backs and see if the noise moves. A bent, uneven wheel will do the same.
Smells travel with the car too
Noises are easier to notice than smells, but smells narrow things down. Hot oil smells sharp and slightly sweet, often behind the wheel. Burnt rubber usually means a belt or a plastic trim touching something hot. A fish-tank smell is coolant. A rotten-egg smell is the catalyst struggling. If your car starts to smell of petrol inside, pull over.
When to stopStop the engine and get help if: the temperature gauge climbs into the red, the oil pressure light comes on, the brake pedal feels soft or spongy, or you smell fuel inside the cabin. These are not the problems to "just make it home" with.
What to write down for the garage
Workshops are faster if you describe the noise cleanly. Three things to note: when it happens (cold start, hot, braking, steering), where it seems to come from (nearside front, under the dash), and whether it changes with speed, revs or temperature. A phone voice memo from the cabin is worth more than you would think.
If you need an idea of what gets checked on test day, our MOT explainer covers the main inspection points. And if your car is a cheap used buy, our under-£5,000 guide runs through the pre-purchase listen-around.
Primary sources for symptom checklists: the AA's fault-finding pages at theaa.com and the RAC's driver advice at rac.co.uk, both of which keep their notes up to date.