Bad vibrations

I have an 05 xterra 4x4. I started having vibrations above 55-58 MPH but decrease above 60-65 or so. Along with the vibrations there is a dull constant noise. Ive eliminated the brakes, alignment, and balance on the tires as the possible causes(aligned, balanced/and replaced). What im left with I think might be an issue with the driveshaft or U joints, but im hoping that isnt the issue as i would REALLY like to avoid having to go to the dealership and fork out a pint of blood along with a bunch of cash to get it fixed.

Does anyone have any insight, similar problems with their X etc...estimated cost of repair/parts replacement or insight as to what it is/might be causing my truck to shimmy? 0,o