Please forgive my ignorance. I need to know if this noise is normal and everyone here is so very knowledgeable about their trucks.

This truck’s differential (2019 F250 6.7 3.31 gears electronic locking) is very large and obviously has beefy gears. I did wait 1000 miles before towing. The following test was done on smooth asphalt pavement, where tire noise is hardly perceptible. I do have the Fx4 with off-road tires but they are very quiet (for now at least) since I only have 3000 miles on the truck. There is no load carried in truck bed or towing.

With respect to the rear differential - while traveling on level road I noticed that when I let off the accelerator, slowing with no brakes I can hear a mild whine noise. This whine is also noticeable when I am going down hill, again no brakes. Are the gears in the rear differential loading up holding the weight of the truck back? When I get back on the accelerator, the whine almost disappears. I also did this experiment keeping the accelerator pedal steady at 50 mph a level asphalt road. I can faintly hear the whine noise. While still on level pavement, I put the transmission in neutral and the whine completely goes away.

Is this sound normal for a truck like ours? Thanks

 

Mine has a slight whine right around 70mph. It also changes when accelerating or decelerating.

 

Mine developed the whine this summer after towing my fifth wheel on a 3000 mile trip. Does it the exact same as yours, only on deceleration.

I'm going to make an apt for mine at the dealer, never did it before this summer, totally silent till 25,000 miles.

 

A differential gear whine on decel normally indicates pinion depth is too deep. That doesn't necessarily mean there is a disorder or that you'll suffer a gear longevity problem. There is a sweet spot for gear setup that involves pinion depth and mesh clearance between the ring and pinion. You hit the sweet spot and you have quiet gears. A little off and you get whine which can occur on decel, coast, or accel. Way off and it's very loud and will overheat or break teeth. I would take it to the dealer to access the whine and have them weigh in on if this represents a problem. None of us can hear it from the distance of the Internet, so we're just guessing.

 

Thanks for everyones input. I have been towing 9,000 lbs (boat and trailer), and I too noticed it after a summer of towing. I'm curious, if the adjustment on the differential is incorrect, does it already have an established wear pattern to warrant a new ring and pinion gear? Ford can be difficult to deal with at times-every sound is normal to them. I'll make an appointment and have them check it out, at least it will be on record.

 

If the gears are out of specification, they would have to be replaced. Again, I can't hear it so I can't tell if what you're hearing is within a normal range. A slight hypoid gear whine is not abnormal, but it does depend. One thing that can happen with the rear axle is that the pinion crush sleeve can compress from load. When this happens, the axle is pretty normal except for decel where the pinion is pulled deeper into the ring gear and you can get quite a howl.