Body Beating Noise Symptoms And Malfunction Causes


The volume (amplitude) of this noise alters cyclically, coming to you in waves. The frequency of the noise accelerates with the increase in vehicle speed. This noise occurs at certain engine and/or vehicle speeds, within a relatively narrow range. Even weak body beating noises can be noticed easily because of their cyclic loud-and- soft pattern.
How a beating sound is created
There must be two separate sounds for the beating noise to occur:
1.When two separate sounds with slightly different frequencies, A and B, occur simultaneously, their volume varies cyclically, resulting in a beating noise.
2.When the hills (or the valleys) of two different vibration frequencies, A and B, overlap, they produce a louder noise. And when the hills and the valleys of two different vibration frequencies overlap, they produce a softer noise.
The beating noise frequency can be represented as follows:
Frequency A – Frequency B = Beating noise frequency
Those that we are most apt to sense are beating noises with frequencies of 2 to 6 cycles per second, or 2 to 6 Hz.
Although we have discussed body beating noise here in terms of compound sounds, the same concept of cyclic development may also be applied to vibrations, which are the source of sounds.
Main causes
Difference in engine and drive train vibration frequencies (torque converter slippage, or transmission gear ratio).
Difference in engine and tire vibrations (differential reduction ratio).
Differences in engine and auxiliary component vibration frequencies (pulley ratio of crankshaft pulley to accessory pulleys).

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