I think all of our VX's clunk when you put them into gear and I think it's just the gears engaging. If you put it into gear and hear a little ring (like a bell) after the clunk that usually means that something is loose. The other way to tell if your U-joints are going is to crawl under the car, grab the drive shaft and try to twist it. If it twists more than a minute amount they your U-joint is going. If it twists a lot, then it's a miracle that your U-joint is still attached.
"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