Loud humming when cruising or downhill

[socci]

My truck has been making a loud humming noise that sounds like its coming from the front wheels (almost under my feet) when cruising around 35-45 mph and decelerating without brakes (ex. downhill engine braking). When I accelerate the noise seems to go away most of the time. I do not really notice it at all once I get to speeds over 50. I put the truck in neutral while coasting to see if it was exhaust related and it made no difference. When I reved the exhaust while coasting in neutral I could barely hear it the humming was that loud.


Within the last year I replaced all wheel bearings, all ball joints, brakes, and the forward most u joint. The tires have plenty of thread, but I will take a better look at them today. Any help is appreciated.

 

[drdoom]

Is that rig 4WD, RWD, or AWD? If 4WD I would suspect the transfer case or mismatched or worn tires.

 

[socci]

Is that rig 4WD, RWD, or AWD? If 4WD I would suspect the transfer case or mismatched or worn tires.

Sorry, it's a awd 5.0 138k. Would the front diff make that noise if fluid were low? I haven't seen any leaks though.

 

[sulaco83]

Sounds to me like it's a good chance it's the front diff. Definitely check the fluid.

 

[drdoom]

I would check the transfer case fluid as well.

 

[socci]

I would check the transfer case fluid as well.

I was under the impression that fluid was shared with the transmission, am I wrong about that?

 

[drdoom]

It's separate.

 

[socci]

So my drivers side front axle seal is leaking. I am not sure how long its been leaking, but I filled up the diff (which didnt take much fluid) and rotated my tires because the fronts had some wear on the insides, but not much. The noise is noticable quieter now but not gone. Today before the fill it was making the noise at all speeds in all conditions so it was getting worse. The fluid def toned it down a bit, but I was hoping it would be completely gone. I am going to check the transfer case tomorrow and hopefully replace the seal.