Definition of Noise, Vibration, and Harshness

Noise is any unwanted sound, usually unpleasant in nature. Possible sources of noise are the:

- Engine.
- Engine accessories.
- Intake and exhaust system.
- Driveline.
- Wind.
- Road surface.

Vibration is unwanted low to medium frequency movement which may be either regular or random in nature. It may be felt or heard. Possible sources of vibration include:

- Tires.
- Engine.
- Engine accessories.
- Suspension.
- Driveline.
- Exhaust system.

Harshness refers to the ride quality and is very subjective. Reference to 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 that is not subject to control. Mufflers and dampers are used to reduce these to acceptable levels. Four-wheel drive vehicles and vehicles with Traction-Lok(R) differentials produce noise when driven on hard surfaces that would not be found with two-wheel drive vehicles or vehicles driven on surfaces where wheel slip can occur. If the vehicle has automatic overdrive it is important to test drive in both modes. If the driver is new to the type of vehicle, they may think that some sounds are abnormal when the sounds are a function of the vehicle type.