My drivetrain has significant NVH at 1300 RPM in all gears, notably 5th (approx. 47 mph). The dealer promptly replaced the exhaust header/shield that audibly "buzzed" at 1300 rpm. The noise is gone but the harmonics (vibration and harshness) are still there. The "buzz" seems to be lessened by adding passengers/weight. Do any of you have insight?