Ford 2003 Mustang Workshop Manual page 39

A mid-range frequency (200-800 Hz) noise between drumming and whine. Also described as a hum.
Hum
Mid-frequency (200-800 Hz) steady sound, like a small fan motor. Also described as a howl.
Hz
Hertz; a frequency measured in cycles per second.
Imbalance
Out of balance; heavier on one side than the other. In a rotating component, imbalance often causes
vibration.
Inboard
Toward the centerline of the vehicle.
Intensity
The physical quality of sound that relates to the strength of the vibration (measured in decibels). The
higher the sound's amplitude, the higher the intensity and vice versa.
Isolate
To separate the influence of one component to another.
Knock
A heavy, loud, repetitious sound, like a knock on the door.
Moan
A constant, low-frequency (100-200 Hz) tone. Also described as a hum.
Neutral Engine Run-Up (NERU) Test
The operation of the engine through the normal rpm range with the vehicle standing still and the
transmission disengaged. This test is used to identify engine related vibrations.
Neutralize/Normalize
To return to an unstressed position. Used to describe mounts. Refer to Bound Up.
Outboard
Away from the centerline of the vehicle.
Ping
A short duration, high-frequency sound, which has a slight echo.