Initial Inspection and Diagnostic Overview: Overview

DEFINITIONS OF NOISE, VIBRATION, AND HARSHNESS
Noise is any unwanted sound, usually unpleasant in nature. Possible sources of noise are:
- the engine.
- the engine accessories.
- the intake and exhaust systems.
- the driveline.
- electric motors and pumps.
- the wind.
- mechanical pumps.
- the road surface.

Vibration is an unwanted periodic motion of a body or medium. It may be felt, heard, or seen. Possible sources of vibration include the:
- tires.
- engine.
- engine accessories.
- suspension.
- driveline.
- exhaust system.

Harshness refers to the ride quality and is very subjective. Reference to the previous conditions is usually the only way to identify harshness as a symptom.

NORMAL NOISE, VIBRATION, AND HARSHNESS
All internal combustion engines and drivelines produce some noise and vibration; operating in a real world environment adds noise and vibration that are not subject to control. Vibration isolators, mufflers and dampers are used to reduce these to acceptable levels.

A driver who is unfamiliar with a vehicle may think that some sounds are abnormal when actually the sounds are normal for the vehicle type. For example four-wheel drive vehicles and vehicles with Traction-Lok(R) differentials produce noise when driven on hard surfaces that does not result on two-wheel drive vehicles or on surfaces where wheel slip can occur.

As a technician, it is very important to be familiar with vehicle features and know how they relate to NVH concerns and their diagnosis. If, for example, the vehicle has automatic overdrive, it is important to test drive in and out of overdrive mode.