How to Troubleshoot a Car Exhaust or Engine Noise

By nature, the combustion engine is supposed to make noise. Anytime you have a controlled explosion occurring multiple times every second, there are bound to be some sort of racket coming from the engine compartment. Although most of today's advanced exhaust systems are designed to muffle the road noise, there are times when they break, wear out or crack, causing a noisy engine or exhaust situation that typically is an indication of a potentially expensive repair.

However, not all noises are the same; or are caused by similar mechanical component failures. The fact is that there are several different types of noises that are made; each of them contributing to a different mechanical failure.

Understanding the common noises associated with engine or exhaust component failure

In order to correctly identify the noises and troubleshoot their primary source; we've taken the liberty to document a few of the common sounds that a damaged component will make and what typically causes these noises in the sections below.

Whirring

Description of this sound: This noise is associated as a vibration or buzzing sound; similar in many ways to the sound that a window or portable fan makes when it is activated. Some of the common causes of this type of sound are attributed to belts, pulleys, or belt-driven components.

What's the cause of this sound? A whirling sound which changes pitch or volume based on the engine speed is a typical sign of engine related issues. Parts that cause this sound are belt-driven accessories, or the actual belt. Some of the most common component that will make a whirling sound includes:

  • Serpentine belt
  • Alternator
  • Drive belt
  • Power steering pump
  • Water pump
  • Radiator fan
  • Idler or tension pulley

These sounds may be caused by loose belts, bearings that are damaged inside the pulley's or brackets or the pulley itself. In most cases, if the belts and pulley's are in good shape, are tight and not the source of this type of noise, the water pump is the most likely candidate.

Hissing, gurgling, or sizzling

Description of this sound: Essentially, the hissing sound is the sound of vapor or steam escaping a pressurized source. The gurgling sound is typically associated with boiling water and a sizzling sound, similar to that of hot bacon being fried on a griddle.

What's the cause of this sound? In many ways, these three sounds typically are attributed to the same source; an overheating engine or coolant system. When you hear the hissing sound, it's usually attributed to steam that is leaking from the radiator cap, the overflow tanks or a recently created hole in any part of the cooling system.

As the coolant begins to heat above 200 degrees, it starts to boil, which when contained in an enclosed system (like a radiator) will develop excess pressure. Once this pressure gets to a certain "boiling point" it will also make a gurgling noise. Some people say that the gurgling sound is similar to a pot of coffee percolating.

The sizzling sound is commonly the after effect. This occurs after the engine has overheated and is caused by coolant or oil being forced from its containment source and landing on hot exhaust components, the engine block, cylinder heads or the intake manifold. The sizzling sound is also commonly associated with issues with the catalytic converter.

In some instances, the materials inside this component will wear out overtime, requiring this part to be replaced. If excessive heat builds-up inside the catalytic converter, it may often make a sizzling or hissing sound. The sound is commonly followed by a rotten egg smell and will typically exhibit engine inefficiency.

Anytime you hear any of these three sounds, immediate action is needed by the driver to reduce the potential of further damage to multiple engine components. Engine overheating can cause the cylinder head to crack or the gasket to separate causing coolant to seep into the oil chambers and potentially damage internal engine components.

Loud exhaust

Description of this noise: Although a finely tuned-exhaust system is music to most gear heads, the sound of exhaust escaping from the exhaust pipes, manifold or muffler is not something you want to hear. In most cases, this sound is similar to rattling steel inside of a cage or clanking metal. The engine tone will be deeper and it's common to hear periods of engine backfiring when you have an exhaust leak somewhere in the exhaust system.

What's the cause of this sound? When your vehicle sounds as if it turned up the volume on the exhaust by a factor of three to five, it's usually caused by a leak somewhere in the exhaust system. If the noise is coupled by a loss in engine performance, it means that the condition will be closer to the engine as opposed to closer to the muffler.

Some of the more common components that cause this type of sound that may be broken, cracked or have become loose for some reason may include the following:

  • The exhaust manifold
  • The EGR valve
  • The exhaust pipe connection to the manifold
  • The exhaust pipe to catalytic converter
  • Catalytic converter
  • Catalytic converter to muffler pipe
  • The muffler

If you notice this sound, the best way to troubleshoot the source is to crawl underneath the vehicle while it is running to try and locate the source of the exhaust leak. It's recommended to have a professional mechanic complete exhaust system repairs as they usually require specific tools or welding to be done to replace or repair broken exhaust components.

Backfiring

Description of this noise: An engine backfire sounds like a very loud firecracker like an M-80 or a "cherry bomb" exploding out of your exhaust. In some cases, the backfire will actually reverse direction and pop out of the injection system. This is more common with carbureted or turbocharged engines as opposed to the typical fuel injected motors.

The backfire sound can occur in the intake or the exhaust system. If it occurs in the intake system, the noise will come from the fuel system (fuel injector throttle body) and if from the exhaust system (which is most common) will come from the exhaust pipe.

What causes a backfire? According to most professional engineers, a backfiring situation can be caused by water that finds its way into the combustion system. However, the exact source of this condition is incredibly hard to diagnose. The image displayed above this section indicates just a few of the potential components that if faulty or damaged, may cause an engine to backfire.

Although the fuel cells of vehicles on road today are sealed and highly resistant to water finding its way into the engine, the reality is that the fuel we put into the tank may have trace amounts of water. As the humidity climbs, condensation may also find a way into the vapor as air is introduced to the fuel system.

When the fuel to air ratio has a higher balance of water grains, the ignition system may fire later than it should. In most cases, this results in unburnt fuel to enter the exhaust manifold, were hot gases will ignite and cause the backfire to occur. If it occurs on the other side of the engine (the intake side) it may be contributed to a vacuum leak or ignition system failure.

To troubleshoot a backfire condition, it's recommended to contact a professional mechanic and have the mechanic download any error codes found in your engine or exhaust system. Most of the time, this condition will trigger the Check Engine Light to occur.

Sputtering

Description of this noise: An engine sputter is best described as an inconsistent harmonic sound coming from the engine. When an engine is tuned correctly, it typically sounds smooth and definitely not choppy. As the engine accelerates, the engines harmonics are equally smooth. A sputtering engine will rise and fall rapidly, may have periods of stalling or rapid acceleration or deceleration.

What causes this sound? Essentially sputtering is the end result of incomplete combustion. It's typically caused by ignition timing problems including ignition coil, distributor, rotor, spark plugs and spark plug wires. In some rare instances, a sputter issue will be accompanied by a Check Engine Light that illuminates on the dashboard. When this occurs, the onboard computer will trigger an OBD-II error code that is stored in the onboard computer. In order to access this code a professional mechanic will need to attach a digital scan tool to the onboard computer.

On the other side of the equation, a sputter sound may also be contributed by a reduction in fuel flow. In many cases, if the fuel system is to blame, it's caused by clogged or dirty fuel injectors. If you notice this type of sound, there are a few things you can do to troubleshoot the problem.

  • First – download any error codes to pinpoint the source of the Check Engine Light
  • Second – check your fuel injector nozzles to see if they are dirty or clogged
  • Third – inspect your ignition system components for signs of damage, loose fitting wires or signs of condensation (usually inside the distributor cap)

If you complete these steps and still can't find the culprit, contact a professional mechanic as soon as possible to inspect your vehicle for electrical or fuel-related issues associated with a sputtering engine.

Tapping, clicking, or knocking

Description of this sound: Although the engine should run like a finely tuned clock, it shouldn't sound like one as it's running. The noticeable sound of ticking, clicking or knocking is often caused by a metallic tick like something inside the motor is hitting a metal stick against one of the components. As the engine's RPM increases, the ticking or knocking sound will commonly increase as well. The description of this sound is actually the primary source of this issue.

What causes this sound to occur? There are two distinct sources of an engine knock or ticking sound. If the engine ticking or knocking seems to be coming from the top of the engine, it's usually caused by metal to metal contact. In most cases, this is due to a lack of oil in the cylinder head hardware, low oil pressure, excessive valve component clearance or defective hardware in the cylinder head.

The secondary source is often referred to an engine knocking due to premature combustion. As the illustration above displays, a normal combustion is supposed to be smooth and timed specifically as to enhance the combustion inside the combustion chamber for equal distribution of power. When premature combustion occurs, the spark is erratic. This can be caused by ignition timing that is not properly set or fuel that is not properly vaporized.

The best way to troubleshoot this condition is two-fold:

  • If it's an oiling issue, check the engine oil level. If it's low, add oil until it is full and see if the ticking noise goes away. If the oil pressure is the source, you might have to contact a professional mechanic to inspect your oil pump or components that supply oil pressure inside your motor.

  • If this is an ignition issue, have your ignition system timing inspected or set it to the factory's recommended settings. Inspect the ignition system for signs of damage or have the fuel tested to determine if it's "bad."

In most cases, the engine ticking or knocking problem is one of most difficult to solve; especially if it's caused by loose components inside the cylinder heads or the engine. If those parts are not serviced or replaced in a timely manner, it can cause serious engine damage to multiple parts of the engine; including complete engine failure.

Noises in general can be very hard to pinpoint, which is why professional mechanics often will road test a vehicle to try and listen for signs of mechanical damage. If you're able to troubleshoot the exact source of your engine noise, but require some assistance to repair the problem, contact a professional mechanic to diagnose a noise from the engine or exhaust inspection.


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