Woo - first time I've ever posted on anything!

Recently upgraded from '88 240 wagon to my super duper V70, and have since been chasing a very annoying rattle: firstly got the wheels aligned, then wheel bearing on drivers side, engine mounts on other side, new struts on both sides and control arm on driver's side . . .

Still rattles: loudly when cold or turning, quietly but much faster when cruising. Always thought it must be connected to the drive shaft, and behold, while car is up on lift and manually turning shaft back and forth, here is the rattle!

Now, how does one fix such a thing. My mechanic will install a new shaft assembly if I can find it, but he doesn't promise that it's not a tranny problem. Any hints? And how does the word U-joint come into all this??