Identifying noises that should be considered a normal characteristic or a mechanical defect can be a challenge, even for the most experienced technician. Some engines, systems and components come with their own noise characteristics that we would once consider a defect, but now are considered a normal characteristic. Some mechanical failures may not receive immediate attention, as the technician may put them into a normal characteristic category. Consider the following when diagnosing an engine noise complaint or when a visual observation identifies a condition that reflects a mechanical failure, often before performance symptoms are evident: