Hello Kidroff,if you look up in the shoe in front of the bottom sieve you will probably find a round hole screen.These are sometimes used for small grains,just take out your seives and remove the round hole screen.
I had the same problem on a 750. Never did find out why it suddenly seemed to start doing it but I "fixed " the problem by putting a piece of sheet metal on the Thistle wires on the back of the grain pan.