I have an 08 RZR 800 with an issue. There is a banging sound that you can also feel in your feet that will occasionally bang. It does it more at speeds above 35mph and when making right turns (occasionally left also but a lot more on right turns). I let everything get good and dirty and drove it around after it dried. My thinking was that if something externally was hitting something (which is what it sounds like), there would be "clean" marks. I then pulled it up on my lift and looked under the front end. The front of the driveshaft at the area of the u-joint knuckles had "clean marks" on them like they had been hitting the steering mechanism right above them. I grabbed the driveshaft with my hand (after removal of skidplate) and thete is a lot of play in it. Almost an inch of movement! The male pinion protruding from the gearcase has a tiny bit of movement and looks like its teeth looks fine, from the part you can see. The u-joints also look fine. The female part of the knuckle that sits on the pinion has teeth that also looks fine. The movement is between the female and the male connections. (There is a pin that is in the female part that I would assume engages in a groove on the male pinion part, the pin is still there too.) It is almost like the male pinion is too small for the female end on the drivesaft knuckle. I cant see any break anywhere in the knuckle. Other than it sounds and feels like the front end is exploding and coming apart at the seams, it drives and operates normally in both two and four wheel drive. But I'm scared to drive it much at all.