Ya actually if you take the joint apart, you will see grooves worn into the cup that the ball bearings sit in. And when you turn the wheel, the ball bearings will slide in and out of the grooves causing the clicking noise.
The most common cause is lack of lubrication. Either a boot gets torn or there wasn't enough grease in there to properly lubricate things. I've seen CVs go for 200K miles easily with multiple boot replacements and still work fine. Even on cars driven by teenagers.