front end drivline noise

Need a little help here. 99' classic, 60k miles. I have developed a new noise in the front end, and it is definately a driveline noise. The noise can't be heard at low speeds, but as you reach highway speeds it becomes more apparent and hits a resonance frequency at about 67mph. I would describe it as a low rumbling noise, like a bad set of tires would sound...except it just started doing it all of a sudden. Tire pressure is good, gear lube is good (checked it because I had driven through some water on a trail a couple of times). Could this be a carrier bearing? Backlash on the gears? Any info would be greatly appreciated!

possible front carrier brgs. but its easier to remove the front hubs and check those bearings first, once removed from the vehicle just turn the hub inside of them. if it grinding or grabbing they are bad

Your first step is to pull the front driveshaft and see if you still have noise.
If the noise is gone, then rebuild the ds or have it rebuilt and balanced.
If the noise is still there, I would look to the hubs for a 'grinding' noise.
HTH