Vibration/Harmonic noise at highway speed?

[1999-Intruder]

I am trying to diagnose a problem with a 93 4x4 (manual all) ranger 3.0V6 5 speed.
Here is what happens:
At Highway speed starting about 40+ we hear a humm/Harmonic noise that sounds something like bearings that have failed. It is a low harmonic not a high pitch and it is loud enough at 55 to piss us off. It does it with the engine off and clutch engaged or disengaged. It does it in or out of 4 wheel, and also with the transfer case in neutral and the truck going 50 with engine off. It does diminish in intensity after about 65+. Sounds more to be in the front than the rear but this is a guess.

Here is what we have determined not to be the problem:
We have disassembled both wheel bearings on the front and the hubs are brand new. The drive shaft has been swapped for the one piece so the shitty carrier bearing is gone. brakes are checked and u-joints are fine. alignment has been done, and tires are in great shape and balanced. Wheels are stock. no leaks in transmission or t-case but not sure if there could be something else wrong internally.

Any thoughts or infromation would be greatly appreciated. Thanks ahead of time.

RANGERS RULE!!!

 

[Big Jim M]

Tires are most times the problems with these noises and vibrations..
WHO balanced them? I get mine done at the local FORD Dealer...same price and always a better job!
Have you rotated the tires? Sometimes the front get just a little bit of wear and start making noise..
I have even changed tires/wheels temporarly with a friend to find my tire tread was the problem..
Big JIm

 

[1999-Intruder]

I will suggest the "rotate tires" to him, He got them balanced at schwab. (i hate that place). I was thinking that possibly the transmission is going bad, but those M5's are practically bullet proof.

 

[suprapsu]

Did you ever figured out what was the problem?

 

[1999-Intruder]

No we never did figure out what the problem was. And now I don't even remember if the problem went away or it was still there we we sold the truck. But I honestly would start by replacing that junk 2 piece drive shaft, you can get them pretty cheap and it is something that should be done anyway.

We never did try axle bearings. The rear axle bearings could have been worn as well. This truck had been abused.