This Preliminary Information communication provides information to the technician on the steps to diagnose and repair vehicles that may have a buffeting vibration and/or drone type noise, exhaust tone change, and/or body pressure booming. The concern may be most noticeable while the engine is operating in 4-cylinder Active Fuel Management mode in the 1,100-1,400 RPM range. If the noise is excessive it may excite the roof sheet metal and compound the issue, if this concern is found refer to the latest version of PIT5318. If the concern is qualified to be present during V4 mode operation, but is deemed to be normal by comparing to a like vehicle, then no further repairs should be made, as this is a normal characteristic. If the concern is qualified to be present during V4 mode operation, but is deemed excessive by comparing to a like vehicle then continue with the direction in the Preliminary Information. Vehicles equipped with the 6.2 liter engine and noise cancellation, the noise cancellation may not be working or working incorrectly this can be the cause of the issue. Technician should inspect for aftermarket audio components, objects blocking the microphones or speakers, Diagnostic Trouble Codes B0560, B1277, B127C, or B127D. By the technician pulling the fuse for the amplifier the noise cancellation will be disabled if the noise improves there may be an issue with the noise cancellation system. Technician should inspect the exhaust system also. Exhaust should be checked when it is hot and cold while the vehicle is in neutral, forward and reverse gear. Inspect the exhaust system for loose and/or missing fasteners, heat shields damaged, joints and/or couplings not properly seated, bracket and/or insulator mounting concerns, inadequate clearance to body and/or chassis components, improper alignment, disconnected and/or missing insulators, cracked, dry-rotted, and/or oil-soaked insulators, stretched, twisted, broken, torn, and/or collapsed insulators, and bent, twist
