Download Install Exhaust System Flex Pipe Kit ’07-10 GMC Sierra 1500 – Condition Some customers may comment on a moan or vibration noise at low vehicle speeds 40-64 km (25-40 mph) or between 900-1700 RPM under load. Cause Exhaust system resonance may be transmitted through the powertrain mounts into the body causing this condition. Correction Caution: Personal injury or burns may occur when working on a hot exhaust system, let the exhaust system cool off prior to performing the repair. An exhaust system flex pipe kit is available to correct this condition. If diagnosis leads to this condition, install the applicable exhaust system flex pipe kit listed below using the following procedure. Refer to the Parts Information for kit applications and usage. Important: This fix and the kit part numbers are specific to vehicle frame type. A Level 3 frame was introduced interim 2000 model year (approximately January 2000). With a Level 3 frame, the transmission crossmember was moved forward of its previous location. Pre-Level 3 frames will require the installation of additional components to correct the condition.