Visual/Physical Inspection

Inspect for aftermarket devices, which could affect the operation of the vehicle. See AFTERMARKET ADD-ON ACCESSORIES under VIBRATION DUPLICATED, COMPONENT NOT IDENTIFIED under VIBRATION DIAGNOSTIC AIDS.
Inspect the easily accessible or visible system components for obvious damage or conditions, which could cause the symptom.
Verify the exact operating conditions under which the concern exists. Note factors such as vehicle speed, road conditions, ambient temperature, and other specifics.
Compare driving characteristics or sounds, if applicable, to a known good vehicle and make sure you are not trying to correct a normal condition.