A continuous rumble or roar at a constant pitch makes up road noise; the volume of this noise increases with the vehicle speed. This occurs mainly when driving on poorly-paved roads.
1.Main causes
Small bumps or depressions in the road surface
Tires resonating with these irregularities
Vibration of the suspension (due to improper spring constants of the rubber bushings)
2.Mechanics of noise development
(1)When driving over poorly-paved roads, small vibrations are generated in the tires. When these vibrations reach a certain frequency, they produce resonances in the tires which amplify the vibrations.
(2)These vibrations are transmitted from the suspension to the vehicle body, and a roaring is produced from the body panels.