Drive Line Vibration/Moan Noise in Sixth Gear - keywords 6sp axle buzz differential driveline flange high hum M12 propeller propshaft rattle shaft shake

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.

Vibration or noise at highway speeds in sixth gear only.

There are two different but similar concerns with these vehicles.

1. The first one is a high speed vibration that will actually be more of a "noise" rather than something you can feel. Driving the vehicle in fifth gear under the same speed conditions may exhibit trace amounts of this same noise or vibration. This concern is also described in TSB 04-04-17-003. If the paint marks are already aligned, a system balance of the propshaft in the vehicle may be required to improve the concern.
2. A similar symptom is a vehicle that has a first order propshaft speed vibration in sixth gear only. There will be no trace of this vibration in fifth gear at the same road speed. A transmission replacement may be required to resolve this concern.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.