Unusual noises from the engine compartment worry every motorist. It is not uncommon for an unusual noise from the engine to indicate a serious problem with the car. In our guide, we explain what can cause the engine to clack, squeal or rattle. You will also find out how you can get to the bottom of the unusual noises yourself and what you should do to avoid engine damage.

Possible causes for noises from the engine compartment

If the engine in the car makes unusual noises, there are various possible causes. This can be a problem with the valve train or a problem with the auxiliary units. In the worst case, there may be defects in the pistons and cylinders that require quick action to prevent engine damage.

• Valve clearance requires adjustment
• Hydraulic tappets do not work correctly
• Oil supply is inadequate
• Camshaft and valves are worn
• Wear on the timing belt or V-belt
• Faulty alternator or air conditioning compressor
• Components on the engine are loose
• Cylinders or pistons are defective

Not all noises from the engine area are also caused by the engine. Drivers should pay attention to whether the noise depends on the engine speed or the speed. However, unusual noises depending on the engine speed often indicate an engine problem.

Vehicle-specific noises on the engine

Certain noises occur more frequently with some vehicle models or engines than with others. Model-specific noises are not uncommon. For example, certain BMW vehicles sometimes make howling noises after starting. These can be caused by defective pulleys in the power unit. Engines from the Volkswagen Group, on the other hand, are often plaged by a rattling noise that is caused by a stretched timing chain.

If the auxiliary unit makes a noise

The drive unit itself is not always the cause of an unusual noise. The numerous auxiliary units of the engine can also make noises if they are not working optimally. These include the alternator and the power steering pump, but also the air conditioning compressor or the water pump. Worn drive belts of the auxiliary units, such as V-belts or V-ribbed belts, are also possible causes.

Other parts can cause noise

In some cases, an annoying noise sounds as if it is coming from the engine, but in reality the causes lie somewhere else entirely. For example, noises such as a rattling in neutral can also come from the clutch. The rattling of broken clutch springs then sounds as if the engine is rattling.

Sometimes there are loose parts on the car, such as a heat shield on the exhaust, that only vibrate at certain engine speeds and frequencies. This sometimes sounds as if the noise is coming from the engine. Defects in the gearbox or drive train can also be the cause of the noises.

Unusual noise on the engine – these noises exist

If the car makes unusual noises, most drivers notice them immediately. Not all noises immediately indicate a defect. For example, a ticking engine with the bonnet open can also be caused by the normal ticking of the fuel injection. Other noises, however, occur far more frequently and should be given special attention.

• Clacking of the engine
• Squeaking from the engine compartment
• Rattling noises
• Engine rattles

Noises such as clattering, rattling or squeaking should be taken seriously in any car. There may be a serious problem with the engine that could eventually lead to engine failure. The cause of the noise must be investigated promptly. If you are not an experienced mechanic, you should visit a workshop as soon as possible.

When the engine clacks

If the engine makes a metallic clacking noise, it is not always possible to pinpoint the cause. Possible causes can be worn alternator bearings, but the noise can also come from inside the engine. In this case, the hydro tappets on the valves may be the cause.

These hydraulic tappets or valve lifters are mounted between the camshaft and the valve, where they regulate the valve clearance. The hydraulic tappets are particularly sensitive to fluctuations in the oil supply. If the clacking does not disappear shortly after starting the engine, the valves and hydraulic tappets should be examined more closely.

Squeaking from the engine compartment

A frequently occurring noise in combustion engines is squeaking. The noise can occur continuously while driving or is only perceptible when accelerating. Squeaking noises are often caused by the V-belts. If the belts installed here are worn and in poor condition, they can no longer drive the auxiliary units such as the alternator properly and slip over the belt pulleys.

Engine rattle

A rattling engine often occurs when there are problems with the timing chain. Often the timing chain has elongated with higher mileage, which is why the rattling noise can be heard. However, the tensioner of the timing chain may also be worn, so that it is no longer properly tensioned. Certain engine types are more prone to rattling noises than others.

Unusual noises from the engine – what motorists can do

Only expert car mechanics should carry out diagnoses or even repairs themselves if the engine makes an unusual noise. However, troubleshooting is never wrong. This not only helps to find the cause of the noise. The mechanic in the workshop can also isolate the cause of the fault more easily with this information.

1. Take a test drive: When driving on a level and straight road, the noises in the car should be analysed more closely. Is the noise dependent on the engine speed? Does it also occur when the clutch is pressed? If so, it is more likely to come from the engine than the drive. However, if the engine not only sounds unusual, but warning lights also light up in the dashboard, it is better to switch off the engine and tow the car away.
2. A look under the bonnet: A look into the engine compartment not only reveals defective engine parts. It is also sometimes easier to determine the cause of the noise than while driving. To do this, a second person in the car can press the accelerator pedal. Is the noise coming from the alternator or directly from the engine? This can often be checked by ear.
3. Check fluid levels: If the oil level or the level of the servo fluid is not correct, the engine or servo pump may tend to make noises. The lack of oil supply can not only be the cause of a clacking engine. In the worst case, the lack of oil leads to a seized piston and thus to capital engine damage to the car. If the oil level is low, engine oil must be topped up. If the unusual noises persist, a workshop should be contacted.
4. Inspect the belt: A worn drive belt is often the cause of unusual noises such as squealing. With the engine switched off, the V-belts of the auxiliary units can be checked for wear. Sometimes it is just a question of the necessary belt tension. On older vehicles, the belt can be retightened; on a newer car, it may be necessary to replace the belt tensioner.
5. Check valves and camshaft: Experienced car mechanics can inspect the valves and camshafts after removing the valve cover. Defects and possible causes of engine noises can sometimes be found here. If necessary, professionals can adjust the valve clearance or replace the valve tappets themselves; everyone else should take the car to a workshop.