We've had the same problem. Check front bolts on the rail that holds the top seive, check all the sides of the combine. They develope cracks in the side and flex. There is an update kit from Case, two cast iron (bow tie) looking metal pieces that you bolt on the sides to stop the flexing. There are 4 bolts on the top seive in the back, two on each side, one short and one longer. Get on Cases website, www.cnh.com and look at parts, see an exploded view to show you where they are. Ours is still holding up since doing the update. By the way, we replaced it with lowen chaffer, from Abilene Machine. Greg