Ford has a Technical Service Bulletin that may apply. (TSB #05-23-3) I would have a Ford Dealership inspect the vehicle and see if this TSB fits the description of your problem.
Rear Axle Noise Repair
Some vehicles may exhibit an axle whine or hum during acceleration, deceleration and/or cruise.
Action: An axle repair kit has been developed which incorporates most parts required for a comprehensive axle repair. The kit should be used instead of installing a complete axle assembly to repair an axle whine/hum. Replace Ring and Pinion gears with Axle Kit components.
Wednesday, October 5th, 2011 AT 10:10 PM