Just to eliminate one aspect of the drive shaft; just crawl under the VX and grab the drive shaft and see if you can twist it. If there is some play in it then look at the front and rear u-joints to see if you can see where the play is happening. That will be the down and dirty, super easy way to tell if it's one of the u-joints. If there isn't any, or not much, play in the drive shaft then grease the zerk fittings (or have them greased). Doing this has eliminated many members drive line noises (for a while at least). There is a zerk fitting on each of the u-joints and one in the middle of the drive shaft at the slip joint.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless