Humming Noise and Vibration

[Bugsy]

Hello all,
This is my first post so I hope I get it right.
I have a humming and vibration at about 55-60 MPH when I'm in 4-wheel drive HI. Sounds like it is coming from the front. Both axles were serviced at 100 miles and are full with the right fluid. Normally in 2 wheel drive I have the same noise at the same speed but very faint and not aggravating like 4-wheel. Does not sound like tires but a bearing noise. Not sure.
It will fade away at higher speeds.
Truck has 9,500 miles.
By the way,two injectors replaced at 8,000 miles!
Also, the truck had half the rear axle fluid from the factory and the grease joints must have been near dry. It took a bunch of grease just to get the boots to move. My friend works at FORD and he told me to do a complete lube on the truck as soon as I got it home. Glad I did. He works at FORD so I wonder what that implies? :)
2004.5 Silverado 2500HD, D/A
Completely stock.
Bugsy

[More Power]

Welcome to the BB!

The humming is probably due to a very slight imbalance of some 4WD related component. This can cause a sympathetic vibration to occur, which manifests itself as either a felt or heard hum/buzz. I doubt you have a problem that needs attention - there's just a lot of mechanical stuff spinning up there while in 4WD.

Being old school, I tend to not want to run in 4WD at anything approaching typical highway speeds. And, especially not on road surfaces that don't need 4WD (unless at the 1/4-mile track ;) ).

MP