I have an 07 Sportsmand 800 that I just purchased about a month ago.  It was a carry over from last year and felt like I got a pretty good deal on it.  I have one question though:  It seems to really clatter like there is a problem with a U-Joint or something in the drive train.  I called the service department at the dealer that I bought it from and they tell me that the clattering noies is normal.  Does anyone else have this noise going on with thier Sportsman?  Any replies are appreciated.  Thanks.  

I did the same thing 2 years ago with an 05' model I got half way thru 06'.
Does it mostly do it when you let off the gas? Does it sound like it is downshifting somewhat? Or does it do it at idle and when you rev it up out of gear?  

I have an 08 sportsman 800 and it does the same thing. Not sure what it is yet.  My dealer says it's normal.  Although I am having the Polaris rep. take a look at it to see if it is a factory flaw. Sounds like it is the same problem as your.