Finally got some free time to get back to this.
I pulled the D/S off again, and cleaned out both U-joint fittings, repacked w/ grease. Did get it coming out the bearing caps on the ends. old stuff was black and thin, new now nice and thick/blueish (synthetic).
Unfortunately, the noise remains. It's not quite as loud, but definitely still there.
With the new grease, the U-joints flop around quite easily, gravity alone will pull them around. On one I *think* I can detect a very small side/side motion but *if* it's there it's subtle. I am kind of out of ideas as to what could be doing this - am I stuck w/ just replacing both joints/ I'm sure they're original.
Just one other thing... any idea just how much grease should be on the inside of the slip yoke/driveshaft? There's a fitting up at the top... when I had it out, I made sure there wass some in it, and greased the ouside of the yoke... looks like you could fit a nearly a whole can inside of there, but I don't see what good that would do you?