Removed my driveshaft today (98z A4), and the u-joints looked fine. The I fiddled with the yoke or whatever that thing is on the rear/differentely that the u-joint connects to and noticed that there's some play there. I'm guessing there's just some play in my gears. Is this serious? How hard is it to replace gears if I really want to fix this?

Another thing I noticed. When I twist the yoke until it stops one way or the other, the clunk/clank sound it makes almosts comes from the wheels, almost more so that than diff. That's odd... Bear with me, I'm a newbie to working on cars as some can tell from my other posts.