Mechanics

Rattle

A rattle or rattling noise can be one of the most frustrating sounds to find and repair. Rattling sound can be generated by almost any part of the car from the engine to the transmission. The cost associated to repair a rattle can vary between tightening a lose bolt to replacing the transmission. Like with any noise, the first step is locating the region in which the sound is be generated from. A rattle can be generated when the car is in motion or when the engine is running with the car stopped. If a rattle is consistent with the engine speed it could be generated by an engine accessory like an alternator. 

If the rattle sound is related to vehicle speed the noise can be generated by a suspension component like a sway bar link. Interior rattles can be difficult to determine when the noise is coming from the internal workings of the dashboard. Other rattle sounds can be created when a system is engaged and then stops again when the system is switched off such as an air conditioner. Below, there are two separate sections the first section includes "engine running, car not moving" and the other section features the "car moving" section. We have list common problems below:

Rattling Noise
Rattling Noise

Car Repair Guide

Engine Running, Car Not Moving: This section includes symptoms that present themselves when the engine is running only.

Checking Engine Oil - Your engine relies on engine oil to supply lubrication the inner moving parts of the engine. If this oil level is allowed to become insufficient (low oil level) the engine cam followers or lifters will lose pressure allowing excessive clearance in the valve train causing a rattling noise. Also as engine oil levels further degrade the engine rod, piston and crankshaft bearing can become damaged allowing clearance producing a rattling sound. Check the engine oil level and add oil as needed to obtain the proper engine oil level. (Note: If the engine oil level is low and your engine is rattling even after you have added oil permanent damage could have occurred and repair or replacement is required)

Inspecting the Catalytic Converter - Since 1976 all cars have been equipped with a catalytic converter which helps burn unused fuel from the exhaust system. This device has been instrumental in air quality improvement. When a catalytic converter fails the ceramic martial inside the converter will shatter into small pieces. If this condition occurs it will create a rattling sound when the engine running in the exhaust system. To check for this condition shut the engine off, using a rubber mallet give the catalytic converter is small rap and listen for a rattling noise. If the catalytic converter rattles it has failed internally and replacement is required.

Check Engine Accessory Mounting/Condition - When your engine starts it provides power to various accessories such as the water pump, power steering, air conditioner, alternator and air pimp (if equipped) These accessories are held in place by mounting brackets and hardware. If the mounting bolts become lose or have broken it will create a rattling noise. To check for this condition inspect the mounting bolt condition in the area in which the sound is being generated. Also check the condition of a particular accessory, look for obvious defects such as a broken mounting hardware, housing or case. If a rust colored powder is present suspect failure near and around the accessory in question.

Check Timing Belt or Chain - Your engine is designed to utilize a timing belt or chain to rotate the camshaft that controls intake and exhaust valve operation. If this belt or chain becomes lose or is failing it can cause a rattle noise that will follow engine RPM. To check for this condition on a timing belt engine remove the timing belt front cover and using a flashlight check for component failure such as a timing belt tensioner bearing or a timing belt that has started to come apart and contacting the outer cover.

Check Engine Flex plate (flywheel) - If your car has an automatic transmission the engine utilizes a flex plate. This flex plate is connected to the engine crankshaft and is used to allow the starter motor to engage and crank the engine over. If this flex plate becomes fractured or is lose to can produce a rattling noise. To check for this condition remove the flex plate cover and inspect the flex plate. Look for rust colored powder either at the crankshaft bolts or the torque converter mounting bolts. Also look for obvious cracks or missing/lose bolts. If any of these conditions occur repair or replacement is necessary.

Inspecting Clutch - If your car is equipped with a standard transmission a clutch assembly is used to disengage the engine from the transmission. If component fails it can allow parts of the clutch to become dislodged creating a rattling sound as these parts are thrown around the bell hosing of the transmission. This noise can change as the clutch pedal is engaged and disagreed. If this is the case with your car the transmission and clutch assembly must be removed to repair or replaced as needed.

Inspect Harmonic Balancer - The harmonic balancer on your engine is used to help silence engine vibration by utilizing a rubber mounting metal ring attached to a hub that is connected to the front of the engine. If this ring becomes dislodged because the rubber insulator has failed it will allow the outer ring to bounce and jump on the rotating hub. This condition will produce a rattling noise that change with engine speed. To check for this condition remove the multi rib belt and check the harmonic balancer condition. If the outer ring is lose replacement is required.

Failed Harmonic Balancer
Failed Harmonic Balancer

Check Clutch Fan Operation - The clutch fan on your engine is designed to engage and disengage as the engine heats up and cools down. If this component fails it can allow the main shaft of the clutch fan to have excessive clearance allowing the main housing to bounce producing a rattling noise. To check for this condition (engine off) grasp the fan blade and check for excessive movement. Usually this condition will be accompanied by the engine running hot or overheating, but not always. The clutch fan should also be able to turn in either direction if any of these conditions occur replace the fan clutch with a new unit and recheck.

Inspecting Dash and Interior Components - Many interior components exist to configure the inner workings of your car. The majority of these components exist in the dashboard including heater-air conditioner ducting and controllers. There are many brackets and braces that are used to hold these components in place. If any of these braces or brackets become lose or broken a rattling noise can occur. The main objective is to locate the point of origin to start the procedure that will repair the problem. Other contributors of interior rattle sounds are the doors. Inside the doors in your car contain window and door latch controls that are used to open and close both the window and door operation. This is done utilizing many structural and mechanical components that can come lose or fail allowing clearances that can produce a rattle. To inspect for this condition the inner door panel must be removed. Once the door panel has been removed check for any brackets or braces that have been broken or any bolts that are missing. Replace or repair as needed and reassemble to recheck.

Rattling Noise When Air Conditioner is On - The air conditioner is designed to operate using a electromagnetic clutch assembly that receives a command signal from the activation switch. This command controls when electricity is supplied to the compressor clutch that engages and disengages the air conditioner system. If this clutch fails or partially fails it can cause a rattling sound. to check for this condition inspect the condition of the air conditioner clutch, it should be intact with no lose moving parts. If the clutch has failed replacement is required. (Note: some air conditioner clutches can be replaced without replacing the entire air conditioning compressor.)

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-16)