Humming or whining noise on a VW or Audi: placing it by how it changes

Almost every hum or whine can be placed without touching a spanner, because the noise tells you what it is by what changes it. The single most useful fact is whether it follows road speed or engine speed, and one short test on a quiet road separates the two. Wheel bearings, tyres and a belt-driven pulley or pump are the usual answers on VW, Audi, Skoda and SEAT cars, though they are not the only ones. If the noise comes with heavy steering, a rising temperature gauge, a charging warning light, a smell of fuel or burning, a flashing engine light, or a vibration you can feel through the car, stop reading and read the safety section below first.

The one test that halves the problem

A noise is either tied to how fast the wheels are turning or how fast the engine is turning. Nearly everything else follows from knowing which.

Find a clear, straight, quiet road and get to a steady speed where the noise is obvious. Then dip the clutch or select neutral and let the car coast for a few seconds while the revs fall. Road speed barely changes; engine speed drops a lot. Listen to what the noise does.

Do this only where traffic allows, keep both hands on the wheel, and never switch the ignition off to try it. Switching off takes away the power assistance for the steering and the brake servo, and can lock the steering. A few seconds in neutral is enough. In an automatic or DSG, selecting N briefly while rolling is fine; select D again while still moving, and never touch P or R.

Then do the stationary half. Handbrake on, neutral or park, engine running, and gently raise the revs - a few hundred rpm above idle is plenty, there is nothing to learn from labouring it. If the noise appears and rises with the revs while the car is not moving, it is engine-side and you have already ruled out half the possible causes.

• Noise unchanged while coasting, then fades as you slow down: it follows road speed. Go to the wheels, tyres and driveline.
• Noise falls away with the revs while you are still doing the same speed: it follows engine speed. Go to the belt, pulleys and pumps.
• Noise present at a standstill when you rev it: engine speed, confirmed.
• Noise there at a standstill with no revving at all, coming and going on its own: an electric pump or fan. Different section again.
• If it does both - clearly there at a standstill and clearly worse with speed - treat it as two separate noises until one of them is proved. Cars are quite capable of developing two faults at once, and trying to explain both with one cause is how people buy the wrong part.

When to stop rather than diagnose

Most humming is a nuisance you can book in for. A few versions are not, and pressing on to get home is how a cheap repair becomes an expensive one or a dangerous one.

Pull over somewhere safe, switch off, and call for recovery rather than driving on if any of these apply.

• The steering has gone heavy, or the whine rises and falls exactly with how hard the steering is working. If assistance disappears while you are moving, do not brake or steer sharply - hold the wheel firmly with both hands, slow gradually and pull over. The steering still works, but it will take far more effort than you expect, and the surprise is what causes accidents.
• The temperature gauge is climbing, there is a coolant warning, or you can smell hot coolant. Stop and let it cool - an overheating engine can be ruined in minutes. Do not open the expansion tank cap on a hot engine; the system is pressurised and will scald you.
• You can smell fuel, petrol or diesel, or you can see a wet patch or drips under the car. Stop, switch off, keep everyone away from anything hot or sparking, and do not drive it to a garage to be looked at. Have it recovered.
• A belt squeal or whine alongside a red battery or charging warning light. On many engines the auxiliary belt drives the alternator and, on some, cooling or steering components as well; if it lets go you can lose several things at once, sometimes including the water pump on the engines where it is belt-driven.
• The hum has become a rumble or a grinding, or you can feel a vibration, wobble or a burning smell from one corner. A bearing that has reached that stage can seize, and a seizure at speed is a loss-of-control event.
• A flashing engine warning light. Flashing, rather than steady, generally means a misfire bad enough to be dumping unburnt fuel into the catalytic converter, which destroys it quickly and expensively. Ease off the throttle immediately and stop as soon as it is safe to.
• The brake pedal has gone long, soft or spongy, there is a brake warning light, or the car pulls to one side when you brake. That is not a hum to diagnose later.
• Anything else has changed in how the brakes or steering feel, even if you cannot put a name to it.

If it follows road speed: bearings, tyres, driveline

A worn wheel bearing gives a steady drone or growl that rises with speed and does not care what gear you are in or what the revs are doing. It often appears above a certain speed and gets rougher from there.

The useful test is loading. On an empty road at a moderate speed, in the dry, weave very gently from side to side within your own lane - this is a soft change of line, not a swerve. Weight transfers onto the outside wheel of each curve. If the noise swells noticeably as weight goes onto one side and quietens as it comes off, that side is the likelier suspect. Treat it as an indicator rather than a verdict: bearings do not all behave the same way, and some get louder when the load comes off rather than when it goes on. Before anyone buys a part, the wheel should be off the ground and checked properly for roughness and play. A noise that ignores the weave entirely is more likely tyres.

Tyre noise is the great impersonator, and it is far more common than people expect. Its tell is the road surface: tyre roar changes markedly between smooth new tarmac, coarse chippings and concrete, while bearing noise carries on much the same. Uneven or feathered tread wear is the other clue. With the car parked on level ground, engine off and handbrake on - and never underneath a car held up by a jack alone - run a hand around the tread from front to back, feeling for a sawtooth edge on the blocks. Keep your hand moving in one direction, because a worn tyre can have steel belt wires poking through.

On four-wheel-drive cars, a whine that changes when you lift off and comes back when you get on the throttle at the same road speed points further into the driveline, at a differential or final drive, rather than at a wheel. That is a specialist job and worth describing accurately when you book it in.

If it follows engine speed: belts, pulleys and pumps

With the car stationary and the revs doing the work, you can narrow an engine-speed whine a long way by switching things on and off and listening for a change. If you open the bonnet to listen, keep hands, sleeves, hair, cables and anything loose well clear of the belt and fans - they are turning fast and some cooling fans start on their own with nobody in the car.

Auxiliary belt tensioners and idler pulleys are the usual answer. They hum continuously, often worst when cold, and the note tracks the revs with nothing else involved. A glazed or wet belt tends to chirp or squeal rather than hum.

Water pumps are driven differently on different VAG engines, by the timing belt or chain on some and by the auxiliary belt on others, and some cars additionally run electric coolant pumps, so there is no single rule. A failing water pump bearing usually brings company: coolant traces around it, or temperature behaving oddly.

The timing drive itself is worth naming, because VAG has used both belts and chains extensively and which one your car has depends on the engine, not the badge or the model year alone. Look your engine code up rather than assuming. A rumble, whine or rattle that seems to come from the timing end of the engine, especially for the first seconds after a cold start, is not a wait-and-see noise on either design - a belt that lets go, or a chain that jumps, will usually wreck the valves and pistons on an interference engine. Get that one looked at promptly.

Diesel fuel pumps whine, and to a degree that is simply what they do. On common-rail engines the high-pressure pump gives a hard whine that rises with revs and load. Older VAG unit-injector diesels, the PD engines, have no common-rail pump at all - they use a tandem pump and cam-operated injectors, and they are loud and clattery by design. On either, what matters is a change from how your particular car has always sounded, not the presence of noise itself.

Similarly, some VAG petrol engines are supercharged rather than turbocharged, and a supercharger whines by design; a turbocharger's note rises with boost and throttle load, not with plain revving in neutral.

• Air conditioning on and off, at a steady idle: a change points at the compressor or its clutch.
• Headlights, heated rear screen and blower all on: a change points at the alternator side of the belt.
• Steering turned to just short of full lock at idle, for a second or two only: a change points at a hydraulic power steering pump. Do not hold it there - sitting against the stop builds maximum pressure and is hard on the pump, and turning a stationary car on dry tarmac strains steering components and scrubs the tyres.
• Nothing changes it, and it is there at any rev range: suspect the belt itself, its tensioner or an idler pulley.

If it changes with steering, clutch or gear

Steering. A whine that grows as you turn and peaks near full lock is the classic hydraulic power steering pump. Check the fluid level in its reservoir with the engine off and cold, and look at the fluid's colour and whether it looks frothy. Low or aerated fluid is a common cause, and a leak is worth finding rather than just topping up. If you do top it up, use only what your handbook specifies - VAG hydraulic systems generally take a particular hydraulic fluid rather than automatic transmission fluid, and putting the wrong one in can attack the seals and cost you the rack as well as the pump. Not every VAG car has a belt-driven pump either; some use an electrically driven pump, and some have a fully electric rack with no fluid at all, so the noise may not track the revs. It varies by model and year.

Clutch, on a manual. Sit stationary in neutral with the engine running. If there is a whine with the pedal up that disappears the moment you press the pedal, the noise is coming from something spinning on the gearbox input side. If there is no noise with the pedal up but a whirr appears when you press it, that points at the release bearing. Either way the gearbox usually has to come out, so being sure which it is before you commit is worth ten minutes of listening.

Gear. If the pitch is the same at, say, 40mph whether you are in third or fifth, the gearbox internals are not making it - but that does not put you back at the wheels and tyres alone, because the final drive and differential also turn with road speed and sound the same in every gear. Wheels, tyres, final drive and differential are all still on the list. If the pitch changes when you change gear at the same road speed, or the whine only appears in particular gears, the gearbox itself is in the frame. Some automatic and DSG gearboxes hum quietly from their own hydraulic pump at a standstill, which varies by box and is often entirely normal.

The hums that ignore both

Some noises track neither the wheels nor the revs. They switch themselves on and off, and that is the identifying feature.

A couple of seconds of hum from the back of the car when you switch the ignition on is the fuel pump priming, and it is normal. Cooling fans running on after a hot drive or in traffic are normal too, and on some cars they are loud. Many VAG cars also run auxiliary coolant pumps, brake vacuum pumps, and gearbox or four-wheel-drive pumps, and some petrol engines run a secondary air pump for a short period from a cold start, typically well under two minutes, which sounds like a drone or a small vacuum cleaner and is expected behaviour.

The question worth asking is whether the noise is timed and independent: does it run for a fixed period, or cut in and out regardless of what you are doing? If so, listening will only take you so far, and reading the car is the faster route.

What the stored fault code adds

Mechanical noises often store nothing at all, so a scan that comes back clean does not mean the noise is imaginary. What a scan does is remove guesswork from the shortlist you have just built.

On many VAG hubs the ABS sensor ring is built into the wheel bearing itself. A deteriorating bearing can therefore sometimes log an intermittent or implausible wheel-speed signal on exactly the corner you already suspect, which turns a hunch into evidence - but plenty of noisy bearings never log anything, so silence there rules nothing out. Charging faults support an alternator diagnosis for a belt whine. Fuel pressure deviation faults support a pump. Gearbox and four-wheel-drive control units log their own pump and pressure faults, and those modules are invisible to a basic code reader that only talks to the engine.

Live data is the part that really earns its keep. Watching the four wheel speeds side by side during a slow roll will expose a corner that reads erratically. Watching charging voltage while you switch the headlights and heated screen on tells you whether the alternator is struggling. Watching requested against actual fuel pressure tells you whether a whining pump is delivering.

That is where VAGPULSE fits: Windows software and a cable for one payment that reads the other control modules on VW, Audi, Skoda and SEAT rather than the engine alone, and shows live measuring blocks while the engine is running, so you can watch a value move as the noise changes.

What to write down before anyone touches it

A garage charges for diagnostic time. Ten minutes of notes can turn an hour of chasing into a straight answer, and it protects you from paying for parts fitted on a guess.

Record the noise as well. A phone voice memo from inside the car with a window slightly open is genuinely useful, and driving slowly past a wall or a hedge with the window down reflects the sound back and often makes the side obvious - somewhere quiet and safe, with the phone mounted or held by a passenger, not in your hand. A passenger listening while you do the coasting test is better still.

• The speed or rev range where it starts, and whether it gets worse from there.
• Whether it is the same in every gear at the same road speed.
• What it does when you coast in neutral.
• Which side of the car it seems to come from, and whether that changes when you weave gently.
• Whether it changes with road surface, with steering, with the clutch pedal, or with the air conditioning.
• Whether it is different cold and warm, and whether it fades after a few minutes.
• Anything done to the car recently, especially tyres, brakes, a belt, or suspension work.

Common questions