Troubleshooting Strange Sounds Coming from Your Automobile
You probably know how your vehicle sounds when it’s running properly. Listening to your car can help you troubleshoot problems. If you hear a strange sound, pay attention and react accordingly.
You hear a high-pitched squeal that stops when you shut off your engine: Readjust or replace the belt. These belts should have about half an inch of play and shouldn’t be frayed, cracked, or glazed on the underside.
You hear a continuous high-pitched sound that may continue after the engine’s shut off: Check the radiator pressure cap. The rubber gasket may be worn.
Something ticks rhythmically while your engine idles: Shut off the engine, wait ten minutes for the engine to cool and the oil to settle, and then check the oil level. If you have enough oil, have a mechanic check the valve adjustment.
If you hear a loud tapping or knocking sound in your engine, pull to the side of the road and call for road service. The source may be a loose rocker arm or carbon buildup inside the engine, but if it’s a loose bearing or a faulty piston, it can destroy the engine.
Mild knocking or “pinging” may be the result of using fuel with the wrong octane rating.
You hear the engine running after you turn off the ignition: Your engine is dieseling. This condition only happens to cars with carburetors. It is usually caused by an idle speed that’s set too high or excessive carbon in the combustion chamber.
You hear a whistling noise coming from under the hood: Check the hoses for vacuum leaks. If the whistling comes from inside the vehicle, there’s probably a leak in the weatherstripping.
The engine idles with an offbeat rhythm: It’s probably misfiring. Turn the engine off and try the following:
If attending to the spark plugs doesn’t help, have a technician check the ignition system with an electronic engine analyzer.
The idling is rough but even: Have a technician check the compression in each cylinder.
Your car makes a loud, abnormal sound: A hole in the muffler is probably the cause. Replace it immediately.
The horn is stuck: If your horn gets stuck, pull the wires to stop the noise, as shown here.

If your horn gets stuck, pull a wire to silence it.
You hear a sound but can’t locate the source: Get an old stethoscope. As shown here, take off the rubber disc and insert a piece of tubing in its place (about 1-1/2 inches will do). Then put the plugs in your ears, run the engine, and move the tube end of the stethoscope around the hood area. The stethoscope amplifies the sound as you near the part that’s causing it.

A piece of tubing and an old stethoscope make an efficient troubleshooting device.
You hear whining or humming sounds on curves: Your wheel bearings may be wearing.
Your tires make a weird, rhythmic sound as you drive: Check inflation, tire wear, and wheel balancing.
You hear squealing when you step on the brake: You’ve probably worn the brake pads down too far. Get them replaced immediately.
If you have drum brakes, brake linings that are glazed or worn can cause them to squeal as well.
You hear rumbling noises coming from under or toward the rear of the vehicle: The trouble could be a defective exhaust pipe, muffler, or catalytic converter; or it could be coming from a worn universal joint or some other part of the drive train. Have a service facility put the car up on a hoist and find the problem.
You hear clunking under your vehicle, especially when you go over a bump: Check the shock absorbers and suspension system. If the sound is toward the rear, your tailpipe or muffler may be loose.

Auto Repair & Maintenance Glossary
accessory belt; drive belt
A V-shaped or flat serpentine belt that’s driven by a crankshaft pulley and transmits kinetic energy to various accessories, such as the alternator, air conditioning compressor, fan, power-steering pump, and water pump.

Auto Repair & Maintenance Glossary
air filter
The element in the air cleaner that removes impurities from the air. Most air filters are disposable, although some aftermarket types can be cleaned and reused.

Auto Repair & Maintenance Glossary
alternator
An engine part that generates electric current that’s stored in the battery and used to start the car and run the electrical equipment.

Auto Repair & Maintenance Glossary
automatic transmission
A transmission that selects gears automatically, either by means of a hydraulic converter and a system of bands and clutches, or with an electronic transmission controller.

Auto Repair & Maintenance Glossary
battery
A box filled with a solution of water and acid called electrolyte. The box contains metal plates that store current generated by the alternator and deliver it to the parts of the car that operate electrically.

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block heaters
Devices that keep the engine warm in very cold weather when a vehicle isn’t used. These are especially important for starting diesel engines at extremely low temperatures.

Auto Repair & Maintenance Glossary
brake booster; power booster
In a vehicle with power brakes, a brake booster is located between the brake pedal and the master cylinder to increase the force applied to the pistons in the master cylinder.

Auto Repair & Maintenance Glossary
brake fluid
The liquid used in the hydraulic brake system to stop or slow the car.

Auto Repair & Maintenance Glossary
brake lines
A system of hoses and metal tubes through which the brake fluid flows from the master cylinder to the brakes at each wheel.

Auto Repair & Maintenance Glossary
brake lining
A high-friction material that’s attached to the brake pad or brake shoe. When the pad is pressed against the disc, or the shoe is pressed against the brake drum, the lining grabs the disc or the inside of the drum, which slows the wheel and thus the car.

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brake shoes
Curved pieces of metal on which are bonded high-friction brake linings that are forced against the brake drums to slow or stop the car.

Auto Repair & Maintenance Glossary
carburetor
A device that vaporizes fuel and mixes it with air in proper quantities to suit the varying needs of the engine. Carburetors have been replaced by fuel-injection systems on most vehicles built since 1990.

Auto Repair & Maintenance Glossary
catalytic converter
A pollution-control device that consumes unburned gas in the tailpipe and reduces nitrogen oxide emissions.

Auto Repair & Maintenance Glossary
clutch
In a manual transmission, a device that disconnects the engine from the transmission to allow the driver to change gears and then allows the engine and transmission to resume contact and turn together at a new speed. In an automatic transmission, a clutch performs a similar function.

Auto Repair & Maintenance Glossary
cold air collector box
A rectangular box that contains the air filter. It performs the same function as the air cleaner.

Auto Repair & Maintenance Glossary
compression gauge
A device used to check the amount of pressure created in a cylinder when the piston is at its highest point and is squeezing the fuel/air mixture into the smallest possible space.

Auto Repair & Maintenance Glossary
coolant; antifreeze
An ethylene glycol or propylene glycol solution that raises the boiling point and lowers the freezing point of the water in the cooling system, prevents rust and corrosion, and lubricates the water pump.

Auto Repair & Maintenance Glossary
cylinder
A hollow, tube-shaped pipe in the engine block in which the piston rides up and down to compress the fuel/air mixture that drives the engine.

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cylinder head
The part of the engine above the engine block that contains the combustion chambers and the valves. The spark plugs screw into the top or side of the cylinder head.

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diesel engine
An engine that burns diesel fuel instead of gasoline.

Auto Repair & Maintenance Glossary
diesel fuel; diesel oil
Fuel for cars with diesel engines. It’s similar to home heating oil, kerosene, and jet fuel.

Auto Repair & Maintenance Glossary
dipstick
A metal stick that’s inserted into a reservoir to check the level of the fluid in the reservoir by means of markings on the stick. The most common dipsticks check the levels of engine oil, transmission fluid, and power-steering fluid.

Auto Repair & Maintenance Glossary
disc brakes
Brakes that have calipers with high-friction brake pads, which grab a brake disc (sometimes called a rotor) attached to the wheel and force it to stop turning, thus stopping the car.

Auto Repair & Maintenance Glossary
distributor
The part of the ignition system that distributes the proper amount of electrical voltage to each spark plug in the correct sequence. This task is now performed electronically on distributorless ignition systems.

Auto Repair & Maintenance Glossary
distributor cap
A cap that over the distributor that has an outlet for each spark plug wire, plus an outlet where the wire from the ignition coil enters the cap to conduct high-voltage electrical current to the rotor.

Auto Repair & Maintenance Glossary
drive train
The path of power from the engine to the drive wheels. Consists of the clutch, transmission, driveshaft, differential, and the axle on which the drive wheels are situated.

Auto Repair & Maintenance Glossary
drum brakes
Brakes that use hydraulic pressure to force curved brake shoes against the inner walls of a hollow metal drum attached to each wheel.

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engine block; cylinder block
The cast iron, aluminum, or ceramic block in which the cylinders and the crankshaft are located.

Auto Repair & Maintenance Glossary
engine control unit; ECU
The most powerful computer onboard a modern vehicle, also called a powertrain control module (PCM). Controls most engine functions and processes signals from the various engine, emissions, and related sensors.

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feeler gauge
A device for measuring the distance, or gap, between two surfaces, such as between the center and side electrodes on a spark plug.

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firing order
The sequence in which the cylinders fire on a particular engine to distribute the shock of combustion evenly and to reduce engine vibrations.

Auto Repair & Maintenance Glossary
fuel filter
A device that removes impurities from the fuel before it gets to the fuel injection system. In fuel-injected cars, the filter is found either in the fuel line under the car, or mounted on the firewall.

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fuel injection
A fuel system without a carburetor that employs an electronic fuel management system to deliver a specific amount of fuel to each combustion chamber in response to changes in engine speed and driving conditions.

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fuses
Fuses protect the electrical components and wiring on your vehicle the same way they do in your home. They’re located in a fuse box (or boxes) that usually are found under or near the dashboard or under the hood.

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gap
The space between the spark plug electrodes. Adjusting this space is called gapping.

Auto Repair & Maintenance Glossary
head gasket
The seal between the cylinder head and the engine block. This gasket keeps the coolant out of the cylinders and free from contamination by exhaust gases.

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hybrid
An alternatively fueled vehicle that combines a small internal combustion engine and an electric motor to get maximum power with minimum emissions and maximum fuel economy.

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internal combustion engine
An engine that works on power released by vaporized fuel and air burning inside the engine itself, rather than on an outside source of combustion as, for example, a steam engine does.

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jumper cables
Cables used start a car with a dead battery by conducting current from another battery.

Auto Repair & Maintenance Glossary
manual transmission; standard transmission
A vehicle transmission system in which gears are selected by the driver by means of a hand-operated gearshift and a foot-operated clutch.

Auto Repair & Maintenance Glossary
master cylinder
A device that stores brake fluid and hydraulically forces it through the brake lines to the brakes when you step on the brake pedal.

Auto Repair & Maintenance Glossary
oil filter
A can-shaped device that screws onto the outside of the crankcase and cleans the oil as it circulates through a vehicle's lubrication system.

Auto Repair & Maintenance Glossary
power brakes
A brake system that uses a brake booster (or power booster) to make braking easier.

Auto Repair & Maintenance Glossary
power steering
A device that uses hydraulic power to help the driver steer more easily.

Auto Repair & Maintenance Glossary
pressure cap
A radiator cap on a coolant recovery system or radiator that allows the cooling system to operate under pressure at higher temperatures for greater efficiency.

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radiator
A device that cools the liquid in the cooling system by allowing it to circulate through a series of water channels that are exposed to air ducts.

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shock absorbers
Devices located near each wheel to cut down the vertical bouncing of the passenger compartment on the springs after the wheels go over a bump or the vehicle stops short.

Auto Repair & Maintenance Glossary
spark plug
A device that delivers an electrical spark to an engine's combustion chamber, igniting the fuel/air mixture that produces the power that drives the engine.

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spark plug gap
The space between the center and side spark plug electrodes, across which the spark must jump to ignite the fuel/air mixture in the engine's combustion chamber.

Auto Repair & Maintenance Glossary
starter
A small electrical motor that causes the engine crankshaft to begin to turn, which starts the engine running and so starts the car.

Auto Repair & Maintenance Glossary
starter solenoid
A device that uses electrical current to start and engage the starter.

Auto Repair & Maintenance Glossary
thermostat
A device that keeps the hot coolant confined to the engine cooling passages to help the engine warm up more quickly. After the engine has warmed up, the thermostat allows the coolant to flow to the radiator, where it’s cooled and recirculated through the engine to prevent overheating.

Auto Repair & Maintenance Glossary
throw-out bearing; clutch release bearing
A part of the clutch, activated by the clutch pedal, that allows the clutch to disengage. If you allow the car to idle in gear with the clutch pedal pressed instead of shifting to Neutral, you can wear out the throw-out bearing.

Auto Repair & Maintenance Glossary
transmission fluid
A thin oil that fills the automatic transmission so that it can run on hydraulic pressure. It’s also found in many power-steering pumps.

Auto Repair & Maintenance Glossary
tune-up
The process of replacing a vehickle's fuel filters, air filters, and spark plugs to ensure that air, fuel, and spark are available in good condition to obtain maximum engine efficiency.

Auto Repair & Maintenance Glossary
water pump
A device that circulates liquid through the cooling system by pumping it from the engine water jackets to the radiator.

Auto Repair & Maintenance Glossary
water separators
A device found on diesel vehicles that removes any water that may have contaminated the diesel fuel.

Auto Repair & Maintenance Glossary
wheel bearings
The inner and outer bearings found at each wheel that cushion the contact between the wheel and the spindle it sits on.