i have a new s680 running with 40' macdon draper in tough wheat conditions and seem to have a feed issue at the front of machine in the feed accelerator area. drum in lowered position, feed accelerator on fast speed, large sprocket on feederhouse drive,has small wire concaves, running concave on 14 and rotor speed at 1000rpm's.customer harvesting soft red winter wheat at 12-14% moisture , 80-90 bushel yield at 3 to 4mph. this s680 has a standard rotor with custom cutter option,not a rice machine and the issue is that the machine has a rumble in the feederhouse- feed accelerator area pretty consistent all the time and when crop toughens in evening seems very evident. customer had a 2010 9870 with same header on it and did not have this problem. trying to figure out what is different about the s680 to cause this issue.