Some customers may comment on vehicle vibrations at highway speeds of 72-85 Km/h (45-55 mph). This vibration is apparent after the vehicle has been parked and disappears while driving.
The vehicle's vibration may be caused by "Tire Flat-Spotting." Tire flat-spotting is a temporary condition caused by the rubber in the tire, and other internal components, flattening out during extended parking (usually 24 hours or greater). Flat-spotting can occur on one or more of the vehicle's tires.
Most standard automotive tires will flat-spot under the above conditions. The degree of the Rat-spotting and subsequent vehicle vibration varies depending on tire design, road surface, temperature, etc.
Driving the vehicle eliminates the flat-spot. However, the number of miles required to eliminate the flat-spot is dependent on the length of time the vehicle was parked under the above conditions and the ambient temperature during driving.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.