Vehicle Preparation

1. Check and verify if the vehicle is equipped with the original equipment, type, size, and brand wheels and tires. If non-original equipment wheels or tires are installed, it may be necessary to substitute original equipment level tire/wheel assemblies to eliminate this factor before proceeding with the NVH diagnosis.
2. Check and set tire pressure.
3. Remove any externally mounted accessories, such as luggage racks, magnetic base, or the antenna, which can cause wind noise that interferes with NVH diagnosis.
4. A tachometer must be used as noted above.
5. Note the fuel level. Some vehicles change in their response to various inputs when the fuel level changes.
6. Try to duplicate the conditions with the customer present, particularly the speed and throttle operation.
7. Find the speed where the concern is most severe.
8. Turn the air conditioning system off and on to isolate air conditioning system impact on the noise. Accelerate gently through this speed to a few mph above it and then coast back down a few mph below it and note if the concern changes.
9. Repeat this procedure, if necessary, to get a feeling for the behavior. Then drive about 5 mph above the speed, put the transmission in neutral and coast down. Note any change in behavior.
10. Try "floating" the driveline by backing off slightly on the throttle at the problem speed. The idea is to unload the axle gears and the universal joints as much as possible. If the concern does not change in all these modes of operation, the cause may be driveline imbalance since the imbalance is not changed by the throttle position.