08 F-250 6.4....Tuned with H&S tuner.
DPF Deleated.
Not sure how to describe this but here goes. When I drive on the highway at around 68-70 mph I get this very low moaning humming kind of noise. It's kind of a pulsing rythem frequency. It's not causing any vibration that I can feel but it's more pronounced when on a very smooth surface with less road noise. If I accelerate slightly it goes away but as I get back at about 70 and just cruise it comes back. The RPM's are steady and there is no affect on the way the truck drives. Can't really hear it with the radio on but this is bugging me cause I don't know where it comes from or what it is. Sometimes I think I CAN feel it in the floorboard through my feet but just very slightly. Like I said I can't describe it other than a barely audibly humming or moaning kind sound.
I'm thinking that maybe it's my driveshaft since its speed related.
Anybody else ever get something like this?
Or know what it might be?

 

Hubs is my thoughts...feel them when you stop, compare both sides or better yet use an infrared thermonitor.

 

Are you talking about the locking hubs on the front wheels?

 

Not that...the wheel bearings in the hubs.

 

You may be on to something and have me going in the right direction. Was just reading about hub assemblies and symptoms of these hubs that are failing including the moaning/humming sound. Will definitely jack up the truck and check all the hubs for looseness or play. I could be in the very early stages of bearing failure. I have replaced a hub assembly before but it was on my wife's Chevy Surburban. When I replaced that one it was already to the grinding noise and it was obvious that it was bad. Replacing the hub was pretty easy on her Surburban.

 

I had one fail at about 55K. My symtoms were crackling like when you shut the truck off and you hear your exhaust contracting because of the heat.

I then touched the rim and it was hot..other side fine.

See if you can take the temp of each hub as well.

 

Well I got home from work today a checked all 4 wheels for play by jacking them up one wheel at a time. All wheels were tight on up and down movement except the right rear wheel.
The right rear wheel had a small amount of play so I'm thinking that bearing may be failing and it may be where my hum is coming from.
Do the rear wheel bearings on these trucks come complete in a hub/bearing assembly like in the front....or do you just buy the bearings?
How difficult is it to change bearings out on the rear wheels.
Anybody got a link I can go to?

 

I will have to do some digging but they are different. Have to pull the axle.

 

I used infarred temperature gun on the hubs of my truck and found no temp difference that would indicate a failed bearing....
Also found out that you can get the whole Hub/bearing assembly but only from dealer.

 

Think I'm gonna check/change the Differential Fluid.
Never has been done...now at 78,000 miles.
Is there a gasket for the cover I need to buy on these 2008's?

 

No gasket. Just silicone.

I did mine at 60K. Do the front at 100K

 

Wheel bearings are easy to do on the rear axle.

 

I have the same thing, with 139K on mine. A couple times I have smelled what I thought were brakes, and mine somewhat comes and goes. I feel it more in my butt than anything. I would have thought a bearing would fail sooner, but after seeing the same symptoms, I am leaning towards a bearing. I have changed mine on my old (and truly missed) 99 SD. Are the newer trucks comparable to do?

Rotated tires, replaced carrier and Ujoints, with no help. Worse from 40-65 MPH. I will check play in each wheel tonight.

 

I have not done the wheel bearing replacement yet on the right rear. (The only wheel that had a tiny bit of play). Will likely just buy the entire hub/bearing assemble from dealer for $169 as that is not much more than paying for bearings, races, and seal anyway.
I'm am also needing to get an axle hub socket but not sure on the correct size. It's the socket with 4 prongs but not positive on the diameter across. The auto parts store had several and just want the right size before I pull the axle out.
Will eventually get around to this work soon but mine is not noticeable unless I'm going 70mph....Won't do it below 70 or above 72...so I usually run about 67-68mph anyway.

 

you should be able to just unbolt the axle and slide it oout.....