On one of our 3 9860 premiums we are having problems with the belts(27) coming off of the drive idler(23). We have had this machine for 3 seasons with no problems. Had dealer come and check everything during season and it didn't help. Everything is running True and straight. Combine is at dealer for inspection and they still can't find anything wrong. I used 5 sets of belts this year.Anyone else have any idea as what could be wrong.