I have a 400 with 960hrs and it has a clunking sound, about the speed if you say clunk over and over.  It happens occasionally on turns, or on strait ways, even on pavement.  No matter how fast or slow I am going, it still makes the sound at the same speed.  
 I believe it is something loose, but I dont know.  Also, there is a bit of play in my front/rear drive shafts, could that be the sound of them chattering?

 Also, does anyone have a shop manual download for the 400 auto?

Thanks, any help appreciated.

-Nick