Your Vehicle: 2001 Ford Escort ZX2 L4-2.0L DOHC VIN 3
Vehicle » Testing and Inspection » Initial Inspection and Diagnostic Overview » Glossary Of Terms (Noise, Vibration and Harshness)  
  Glossary Of Terms (Noise, Vibration and Harshness)  

An increase in speed at less than half throttle.

An increase in speed at half to nearly full throttle, such as 0-97 km/h (0-60 mph) in approximately 30 seconds .

An increase in speed at one-half to full throttle, such as 0-97 km/h (0-60 mph) in approximately 20 seconds .

Ambient Temperature
The surrounding or prevailing temperature.

The quantity or amount of energy produced by a vibrating component (G force). An extreme vibration has a high amplitude. A mild vibration has a low amplitude.

Gear teeth clearance.

Low frequency or low pitched noise often accompanied by a vibration. Also refer to Drumming.

Bound Up
An overstressed isolation (rubber) mount that transmits vibration/noise instead of absorbing it.

Brakes Applied
When the service brakes are applied with enough force to hold the vehicle against movement with the transmission in gear.

Strong noise fluctuations (less than 1000 Hz ) caused by gusting winds. An example would be wind gusts against the side glass.

A low-pitched sound (200-5000 Hz) like that from a bee. Often a metallic or hard plastic humming sound. Also describes a high frequency (200-800 Hz) vibration. Vibration feels similar to an electric razor.


The angle of the wheel in relation to the true vertical as measured looking from the front of the vehicle. Camber is positive when the wheel angle is offset so that the top of the wheel is positioned away from the vehicle.


The angle of the steering knuckle in relation to the true vertical as measured looking from the side of the vehicle.

A pronounced series of rapidly repeating rattling or clicking sounds.

A short-duration high-pitched noise associated with a slipping drive belt.

A repetitious low-pitched sound. A loud chuckle is usually described as a knock.

A sharp, brief, non-resonant sound, similar to actuating a ball point pen.

A hydraulic knocking sound. Sound occurs with air pockets in a hydraulic system. Also described as hammering.

Clunk/Driveline Clunk
A heavy or dull, short-duration, low-frequency sound. Occurs mostly on a vehicle that is accelerating or decelerating abruptly. Also described as a thunk.

Releasing the accelerator pedal at cruise, allowing the engine to reduce vehicle speed without applying the brakes.

Coast/Neutral Coast
Placing the transmission range selector in NEUTRAL (N) or depressing the clutch pedal while at cruise.

Constant Velocity (CV) Joint
A joint used to absorb vibrations caused by driving power being transmitted at an angle.

Controlled Rear Suspension Height
Theheight at which a designated vehicle element must be when driveline angle measurements are made.

Coupling Shaft
The shaft between the transfer case and the front drive axle or, in a two-piece rear driveshaft, the front section.

Cycles per second. Same as hertz (Hz).

Amid-frequency sound, related to squeak. Sound varies with temperature conditions.

A metallic squeak.

Constant speed on level ground; neither accelerating nor decelerating.

The process of a vibrating component going through a complete range of motion and returning to the starting point.

A unit of measurement, referring to sound pressure level, abbreviated dB.

Drive Engine Run-Up (DERU) Test
The operation of the engine through the normal rpm range with the vehicle standing still, the brakes applied and the transmission engaged. This test is used for noise and vibration checks.


Driveline Angles
The differences of alignment between the transmission output shaft, the driveshaft, and the rear axle pinion centerline.

The shaft that transmits power to the rear axle input shaft (pinion shaft). In a two-piece driveshaft, it is the rearmost shaft.

All power transmitting components from the engine to the wheels; includes the clutch or torque converter, the transmission, the transfer case, the driveshaft, and the front or rear drive axle.

Drivetrain Damper
A weight attached to the engine, the transmission, the transfer case, or the axle. It is tuned by weight and placement to absorb vibration.

A low frequency (100-200 Hz) steady sound, like a freezer compressor. Also described as a moan.

A cycling, low-frequency (20-100 Hz) , rhythmic noise often accompanied by a sensation of pressure on the ear drums. Also described as a low rumble, boom, or rolling thunder.

Dynamic Balance
The equal distribution of weight on each side of the centerline, so that when the wheel and tire assembly spins, there is no tendency for the assembly to move from side-to-side (wobble). Dynamically unbalanced wheel and tire assemblies can cause wheel shimmy.

Engine Imbalance
A condition in which an engine's center mass is not concentric to the rotation center, causing excessive motion.

Engine Misfire
When combustion in one or more cylinders does not occur or occurs at the wrong time.

Engine Shake
An exaggerated engine movement or vibration that directly increases in frequency as the engine speed increases. It is caused by non-equal distribution of mass in the rotating or reciprocating components.

Flexible Coupling
A flexible joint.

A drive mode on the dividing line between cruise and coast where the throttle setting matches the engine speed with the road speed.

Mid to high (100-200 Hz) intermittent sound due to air flow. Similar to a flag flapping in the wind.

The rate at which a cycle occurs within a given time.

Gravelly Feel
A grinding or growl in a component, similar to the feel experienced when driving on gravel.

An abrasive sound, similar to using a grinding wheel, or rubbing sand paper against wood.

Steady high frequency (200-800 Hz) noise. Vacuum leak sound.

A steady low frequency tone (50-500 Hz) , sounds like blowing over a long neck bottle.

A mid-range frequency (200-800 Hz) noise between drumming and whine. Also described as a hum.

Mid-frequency (200-800 Hz) steady sound, like a small fan motor. Also described as a howl.

Hertz; a frequency measured in cycles per second.

Out of balance; heavier on one side than the other. In a rotating component, imbalance often causes vibration.

Toward the centerline of the vehicle.

The physical quality of sound that relates to the strength of the vibration (measured in decibels). The higher the sound's amplitude, the higher the intensity and vice versa.

To separate the influence of one component to another.

A heavy, loud, repetitious sound, like a knock on the door.

A constant, low-frequency (100-200 Hz) tone. Also described as a hum.

Neutral Engine Run-Up (NERU) Test
The operation of the engine through the normal rpm range with the vehicle standing still and the transmission disengaged. This test is used to identify engine related vibrations.

To return to an unstressed position. Used to describe mounts. Refer to Bound Up.

Away from the centerline of the vehicle.

A short duration, high-frequency sound, which has a slight echo.

Pinion Shaft
The input shaft in a driving axle that is usually a part of the smaller driving or input hypoid gear of a ring and pinion gearset.

The physical quality of sound that relates to its frequency. Pitch increases as frequency increases and vice versa.

Pumping Feel
A slow, pulsing movement.


Radial is in the plane of rotation; lateral is at 90 degrees to the plane of rotation.

A random and momentary or short duration noise.

Rotary Blade Coupling (RBC)
This part is attached to the rear axle on 4WD vehicles. It includes an internal hydraulic pump and clutch pack to control the torque supplied to the rear axle/wheels. It also has an internal electromagnetic clutch to lock to the RCB for the 4WD ON mode. This unit is not to be disassembled and if necessary a new unit must be installed.

Ring Gear
The large, circular, driven gear in a ring and pinion gearset.

Road Test
The operation of the vehicle under conditions intended to produce the concern under investigation.

A medium-frequency vibration. A slightly higher frequency (20 to 50 Hz) than a shake. This type of vibration is usually related to drivetrain components.

Lateral runout means measuring the movement or "wobble" of a wheel or tire at the sidewall. Radial runout means measuring the out-of-round of the tire tread surface.

Intermittent sound of varying frequency (100-200 Hz) , sounds similar to shuffling through leaves.

A low-frequency vibration (5-20 Hz) , usually with visible component movement. Usually relates to tires, wheels, brake drums or brake discs if it is vehicle speed sensitive, or engine if it is engine speed sensitive. Also referred to as a shimmy or wobble.

An abnormal vibration or wobbling, felt as a side-to-side motion of the steering wheel in the driveshaft rotation. Also described as waddle.

A low-frequency vibration that is felt through the steering wheel or seat during light brake application.

A resonance from flat surfaces, such as safety belt webbing or door trim panels.

Slip Yoke/Slip Spline
The driveshaft coupling that allows length changes to occur while the suspension articulates and while the driveshaft rotates.

A high-pitched transient sound, similar to rubbing fingers against a dean window.

A long-duration, high-pitched noise.

Static Balance
The equal distribution of weight around the wheel. Statically unbalanced wheel and tire assemblies can cause a bouncing action called wheel tramp. This condition will eventually cause uneven tire wear.

A light, rhythmic, or intermittent hammering sound, similar to tapping a pencil on a table edge.

A dull beat caused by two items striking together.

A rhythmic tap, similar to a clock noise.

Tip-In Moan
A light moaning noise heard during light vehicle acceleration, usually between 40-100 km/h (25-65 mph) .

The acronym for the total indicated runout is TIR.

Tire Deflection
The change in tire diameter in the area where the tire contacts the ground.

Tire Flat Spots
A condition commonly caused by letting the vehicle stand while the tires cool off. This condition can be corrected by driving the vehicle until the tires are warm. Also, irregular tire wear patterns in the tire tread resulting from wheel-locked skids.

Tire Force Vibration
A tire vibration caused by variations in the construction of the tire that is noticeable when the tire rotates against the pavement. This condition can be present on perfectly round tires because of variations in the inner tire construction. This condition can occur at wheel rotation frequency or twice rotation frequency.

A noise or vibration that is momentary, a short duration.

Two-Plane Balance
Radial and lateral balance.

Any motion, shaking or trembling, that can be felt or seen when an object moves back and forth or up and down.

A constant, high-pitched noise. Also described as a screech.

High-pitched noise (above 500 Hz ) with a very narrow frequency band. Examples of whistle noises are a turbocharger or airflow around an antenna.

Wind Noise
Any noise caused by air movement in, out or around the vehicle.

The acronym wide-open throttle is WOT.