Model Year Program Name Parameter Diagram Air Induction System Noise Factors Sources of Noise 1.1 Air Cleaner (Cover/Tray/Inlet) 3.1 Aftermarket Modifications 1 Piece-to-piece variation 1.2 Amount of Surfactant Solution (oil) 3.2 Engine Compartment Cleaning 2 Wear & Fatigue 1.3 Flanges: Thickness, Width and flatness 3.3 Filter Change/Cleaning Interval 3 Customer Environment 1.4 Ribs/Convolutes: