This type of noise is felt as a pressure in your ears, and its origin is often unknown to you. It increases in pitch (frequency) with the vehicle speed. It occurs within a relatively narrow vehicle speed range centered around 10 km/h, or around 50 rpm if associated with engine speed.
Inertia due to reciprocating motion of pistons, or imbalance in engine
Unbalanced propeller shaft
Incorrect propeller shaft joint angle
Resonances in the exhaust pipe
Resonances in auxiliary engine components
Vibration due to torsional stresses on the propeller shaft and drive shafts.
1.Propeller shaft joint angle
When a joint angle exists in the propeller shaft, there are two torque fluctuations for every revolution of the propeller shaft. These fluctuations become larger as the joint angle increases.
At certain vehicle speeds these torque fluctuations vibrate the drive train, and are transmitted through the rear suspension arm bushings or springs, causing the body panels to vibrate. This results in the body booming noise.
2.Out-of-balance propeller shaft
When the propeller shaft is out of balance, the centrifugal force created by this imbalance attempts to cause the ends of the propeller shaft to bend outward and revolve in large circles around the centerline of the shaft. Of course this does not actually happen because the propeller shaft is fixed at both ends. However, it does cause the shaft to vibrate once each time it rotates.
This vibratory force attempts to bend the propeller shaft.
This vibratory force is further transmitted through the engine rear mounts, center bearing for the propeller shaft, rear suspension bushings, and to the body panels. The body panels then vibrate, generating the body booming noise.
3.Exhaust pipe vibrations
The exhaust pipe, being long and narrow, is easily vibrated. Another important factor which causes it to vibrate vigorously is that it is attached to the engine, the largest source of vibrations in a vehicle.
When the exhaust pipe resonates with engine vibration, the vibration is further amplified and transmitted by way of the O-rings and muffler clamps to the vehicle body, causing body booming noise. To isolate the problem area you could remove the O-rings one by one.
4.Vibration of auxiliary components
Body booming noise may be related to either the engine speed or to a certain vehicle speed.
This can be determined by the following methods:
1.Does it occur when the engine is revved?
2.Does it occur when coasting?