Diagnosing Engine Noise Using Your Ear and Simple Tools

Updated on October 2, 2018
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

The source of engine noise can be hard to pinpoint just by listening to it.
The source of engine noise can be hard to pinpoint just by listening to it. | Source

Diagnosing engine noise is often one of the most difficult tasks you can deal with. Most of the noises that come from the engine can be described by such words as:

  • ticking:
  • tapping
  • knocking
  • hissing
  • popping

The type of sound doesn't in itself tell you where it came from. Many different parts in and around the engine can produce these types of sounds. For example, a bad:

  • alternator
  • power steering pump
  • vacuum line
  • ignition wire
  • water pump
  • timing chain
  • internal engine component

Parts that move at high speed, like accessory pulleys, valve train components, crankshafts, and pistons, can make it hard to pinpoint the source of a new engine noise.

Here, you'll know how to use some simple techniques to find the potential source using your ear and a few simple tools.

First, the procedure used in this guide will help you separate noise from accessories and noise from the engine; then, if needed, there are procedures for identifying the internal engine part that might be causing the noise.

Subsequent sections outline common engine noises that different internal engine components usually produce when going bad.

Keep in mind that this guide focuses on those noises rising from inside the engine block or cylinder head. You won't find much here about noises produced by misfires, backfires, or engine accessories like the alternator, pump, vacuum line, pulleys, or drivetrain.

So, let's find the source of the engine noise.

Contents

I. Is the Noise Coming From the Engine or the Belts and Accessories?

II. Is the Noise Coming From the Cylinder Head or the Engine Block?

III. Checking for Cylinder Head (Valve Train) Noise

IV. Noise-By-Noise Guide to Cylinder Head Noises

  • Clatter
  • Tapping
  • Puffing

V. Checking for Engine Block Noise

VI. Noise-By-Noise Guide to Engine Block Noises

  1. Bell-like sound
  2. Double Click
  3. Rapping Sound
  4. Ticking When Accelerating
  5. Rod Knock Sound
  6. Knocking

Noise can also come from the torque converter or pump
Noise can also come from the torque converter or pump | Source

I. Is the Noise Coming From the Engine or the Belts and Accessories?

Before you blame the engine for a new noise, try to determine where it's coming from. Follow this simple procedure:

  1. Set the parking brake.
  2. Pop the hood open.
  3. Set the transmission to Neutral (manual) or Park (automatic).
  4. Start the engine and pay close attention to the noise.
  5. Gradually increase engine speed and see whether the noise increases with engine speed.
  6. If the noise doesn't increase with engine speed, it's probably not an engine noise.
  7. If the noise increases with engine speed, most likely the noise is coming from the engine, though if you have an automatic transmission it might come from the torque converter.

Now that you've determined that the noise is coming from the engine, you need to eliminate the belt(s), pulleys and accessories as the source.

If you know the noise isn't coming from the belt or one of the accessories, you can skip this test and go on to the next section.

Most worn-out or loose belts produce a squealing sound. If this is the type of noise you hear:

  • Spray some belt dressing on to the belt. If the noise goes away, the belt is the source of the noise.

Another way to check for belt or accessory noise is to remove the suspected belt.

  1. Remove the drive belt or serpentine belt from the engine.
  2. Rotate by hand each of the accessory pulleys the belt runs on.
  3. If one of the pulleys seems unusually hard, wobbles, or feels loose, most likely that's the source of your noise.
  4. Now, start and idle the engine for a few seconds. Pay attention to the engine sounds. Rev the engine a couple of times. If the noise is not present, most likely the belt or one of the accessories is the source of the noise.

You can use a timing light to help you locate the source of engine noise. This is a timing light with integrated RPM, volt and dwell angle meter.
You can use a timing light to help you locate the source of engine noise. This is a timing light with integrated RPM, volt and dwell angle meter. | Source

II. Is the Noise Coming From the Cylinder Head or the Engine Block?

Once you've determined the noise is coming from the engine, the next step is to know whether the noise is originating from the upper (cylinder head) or bottom (engine block) section of the engine.

The best way to do this is by using a strobe light. This is a timing light you can use, on engine models with a distributor, to adjust ignition timing as part of a tune-up procedure.

You can buy a timing light at most auto parts stores. But if you don't have the light and don't want to buy one, most auto parts store may lend you one.

  1. Open the hood of your car.
  2. Connect the timing light's power clamps to the car battery following the correct polarity.
  3. Connect the timing light's inductive-current clamp to any of the spark plug wires.
  4. Position the timing light cables away from moving engine parts.
  5. Start the engine and let it idle.
  6. Aim the timing light to a dark engine surface and press the light trigger.
  7. Listen to the noise and notice whether the noise occurs at every flash of the light or twice per flash.
  • If the noise happens at every flash, the noise is coming from one of the valve train components. For example:
  • lifters
  • valves
  • camshaft
  • rocker arms
  • If the noise occurs twice per flash, it’s coming from the engine block. For example:
  • crankshaft
  • connecting rods
  • bearings
  • pistons

The next sections will help you pinpoint the specific component that might be producing the noise you hear using your ear.

Unadjusted or worn valves and components are a common source of engine noise.
Unadjusted or worn valves and components are a common source of engine noise. | Source

III. Checking for Cylinder Head (Valve Train) Noise

Cylinder head noises can be easier to deal with, because the head is relatively accessible. It's only covered by a metal top that, in many models, you can take off without the need to remove major components.

Some of the most common sounds you'll hear from the cylinder head are:

  • clatter
  • tapping
  • puffing noises

Start with a preliminary inspection. For this check, it's a good idea to use a mechanic's stethoscope, but you can use a length of hose or a large screwdriver instead.

The video at the end of this section gives you some pointers on using a mechanic's stethoscope or a screwdriver to diagnose engine noises, and removing the belt in order to isolate pulleys or accessories that might be the source of engine noises.

During this check, be careful with moving parts while moving your tool around the engine.

  1. Start the engine, set the parking brake, and set the transmission to Neutral (manual) or Park (automatic).
  2. Open the hood.
  3. Using the stethoscope or one of the other tools, move the tip around the valve cover and cylinder head, being careful with moving components. If you are using a hose or a large screwdriver, press one end (screwdriver handle) against your ear and use the other end to trace the noise around the cylinder head.
  4. Find the loudest point of the noise.
  5. Turn off the engine and remove the valve cover for the cylinder head with the source of the noise.
  6. With the cover removed, start the engine, being careful with the oil being thrown out from the cylinder head.
  7. Look at the valves opening and closing and see if those near the source of the noise operate differently somehow. Press down on the rocker arm above the suspected valve and notice if the sound changes or stops. If it does, you've found the part of the valve assembly with the problem. Check for:
  • Insufficient lubrication
  • Unadjusted valves
  • Damage or wear to the rocker arms, pushrod, or lifter
  • Dirt, sludge, or contamination around the valve, spring, and seal
  • Camshaft wear

IV. Noise-By-Noise Guide to Cylinder Head Noises

Try to match your engine sound to one from the following symptoms described next, to zero in on the potential component(s) causing the noise.

1. I Hear a Clatter Noise

Clatter noises in the cylinder head can be caused by:

  • Poor lubrication
  • Worn valve train components
  • Valves in need of adjustment
  • Bent valves or pushrods
  • Bad hydraulic lifter
  • Worn valve guides

Check first for proper lubrication, then valve clearance and wear.

2. I Hear a Tapping Noise

Tapping noise is similar to clatter noise. Often, the terms are interchangeable, but you may hear this distinctive sound when one or more of the valves begin to "float."

Valve floating may be caused by a bad hydraulic lifter or a worn or broken valve spring. Since a floating valve is unable to close properly, the rocker arm begins to hit the top of the valve stem or pushrod. Also, a floating valve may cause the engine to miss, backfire, or pop.

3. I Hear a Puffing Noise

A puffing noise coming from the cylinder head usually points to a burned valve. This happens when combustion heat breaks a small part of the valve's face, causing combustion pressure to leak through the valve. The leak prevents the air-fuel mixture to burn, causing the cylinder to miss, usually at idle. You may hear the puffing sound at the problem valve, at the throttle body (or carburetor), or the tailpipe.

Watch Out For Moving Engine Components!

When using a mechanic's stethoscope or similar tool, be careful with moving components around the engine. You can seriously hurt yourself.

Worn out journals, bearings, connecting rods and piston skirts can produce bell-like, clicking and rapping noises.
Worn out journals, bearings, connecting rods and piston skirts can produce bell-like, clicking and rapping noises. | Source

V. Checking for Engine Block Noise

Trying to identify engine block noises is a little more difficult than locating noises coming from the valve train. Components are not as readily accessible.

Still, using some practical tests, along with your own observations, will help you close in on the suspect component(s).

Engine block noises may come from:

  • Main bearings
  • Piston
  • Piston rings
  • Piston wrist pins
  • Connecting rods
  • Crankshaft journals

First, try to locate the cylinder where the sound is coming from:

  1. Set the parking brake, and put your transmission in Neutral (manual) or Park (automatic).

  2. Chock the rear and front wheels.

  3. Start the engine and let it idle.

  4. Moving your stethoscope (hose or screwdriver) around the engine block, find the cylinder where the sound seems to be loudest.

    Be careful with moving components as you do this check!

  5. Once you've found the loudest point, disconnect the spark plug wire on the cylinder closest to that part of the block. Check to see if the sound changes or stops. If it does, you've found the cylinder where the sound is coming from.

Bad pistons or piston pins and worn bearings can be hard to diagnose.
Bad pistons or piston pins and worn bearings can be hard to diagnose. | Source

VI. Noise-By-Noise Guide to Engine Block Noises

Using the following engine noise symptoms, try to identify the one similar to the noise coming from your engine block. Carefully read the diagnostic description and see if it would apply to the sound coming from your engine. Take into account what you know about the noise, your car's maintenance history, and any problems your engine may have experienced or is experiencing now.

1. I Hear a Bell-Like Sound

A bell-like sound coming from the engine block is usually called "piston slap," but some may describe it as "piston knock" as well.

This is a metallic sound produced by the piston as it slaps back and forth against the cylinder wall. You'll hear this sound mostly when the engine is cold. The sound will increase in pitch as you accelerate.

Causes for piston slap:

  • Worn piston skirt
  • Worn cylinder wall
  • Damaged piston

Once the engine reaches operating temperature, the sound seems to go away.

2. I Hear a Double Click

A metallic, double-click type of sound is usually heard with the engine at idle or at low speed.

Causes for a double-click sound:

  • Worn piston pin (also called a wrist pin)
  • Poor lubrication
  • Connecting rod wear
  • Worn bearings

3. I Hear a Rapping Sound

This sound is more like a sharp, metallic rap coming from the engine block.

Causes for rapping sound:

  • Worn piston pin or bushing
  • Poor lubrication

Most likely you'll be able to hear the rapping sound with the engine at idle and at operating temperature.

4. I Hear a Ticking Sound When Accelerating

Some describe this engine noise as a ticking, clicking, chattering or a high-pitched rattle. It can become noisier during acceleration.

Causes for a ticking sound:

  • Worn piston rings
  • Broken ring lands
  • Worn cylinder wall

Usually, a loose or broken piston ring can be diagnosed with a leak-down test.

5. I Hear a Rod Knock Sound

This is perhaps a tricky sound to identify. A rod knock usually comes from a worn rod bearing, which can produce a light tap or a louder metallic knock sound. And it's usually heard with the engine at idle or at a slightly higher engine speed.

Causes for a rod knock sound:

  • Worn rod bearing
  • Worn crankshaft
  • Poor lubrication

A quick-and-dirty type of diagnostic is to briefly step on and release the accelerator. You'll hear the sound increasing in volume.

6. I Hear the Engine Knocking

This type of knocking sound is heard as a dull, steady knock, most often when the engine is cold and louder during acceleration.

Causes for engine knocking:

  • Worn main bearings
  • Worn crankshaft

Low engine oil level is a common source of engine noise.
Low engine oil level is a common source of engine noise. | Source

Conclusion: Using Engine Noise as a Diagnostic Tool to Understand Your Engine

Diagnosing engine noises is not an exact science by any stretch. Even for experienced car technicians, knowing what's wrong with an engine just by listening to it is difficult. But engine noise can be a useful diagnostic tool.

The techniques presented here will help you trace the source and help you get a closer understanding of the problem.

Don't ignore those noises or expect them to go away. Try diagnosing engine noises as soon as possible. A simple tick can turn into an expensive repair without warning.

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