GMC chervolet camaro 1999 Service Manual page 54

General Information
Moan or Drone
Moan or drone is a sustained tone at a low frequency
of 60-120 Hz, somewhat higher than boom.
Examples of similar noises include a bumble bee or
blowing air across the top of a soda bottle. A customer
may use the following words to describe moan
or drone:
• Humming
• Buzzing
• Resonance
Moan or drone may be accompanied by a perceptible ·
buzzing vibration. Inspect the following systems:
• The powertrain mounts
• The exhaust system
Howl
Howl is a noise at mid-range frequency of
120-300 Hz. This sounds like the wi.nd howling.
Whine
Whine is a prolonged, high-pitched sound in the
300-500 Hz range. Whine is usually related to the
meshing gears or gear noise. Similar sounds include
mosquitoes, turbine engines, and vacuum cleaners.
Vibration Diagnosis and Correction 0-51
Matching Frequency to Component RPM
At this point in the diagnosis, the vibration has
gone through the following analysis:
• The vibration has been duplicated.
• The vibration has been designated as abnormal.
• The vibration has been related either to engine
speed or to vehicle speed.
• The vibration has been assigned a frequency from
the EV A or identified based on its feel or its sound.
Automotive vibrations are usually related to the rotating
speed of a component. Calculate the speed of these
components using either an engine speed method or a
vehicle speed method. Use the engine RPM readings
taken during the road test in order to diagnose the
vibrations that are sensitive to engine speed.
If the vibration is sensitive to vehicle speed, determine
the rotational speed of the tires. As long as you
operate the vehicle at a constant speed, the tires will
operate at a constant speed. This speed is measured
in rotations, or cycles per second. The reading is
then compared to the frequency of the vibration, which
is also measured in cycles per second.