Sounds like the bearing in front is going out, or the front shaft got bent or is cracked and coming loose. If it is the bearing it isn't to huge af job, support the front of rotor and remove bolts on either side of housing not sure if you need to remove feeder housing to do this. Replace bearing and be sure to check front shaft alignment the main cost would be the new bearing unless you find other things wrong. If a rock went in or large slug it could have tweeked the shaft but I doubt it. Also I have a 1982 1480 electric over hyd. with chopper,rock deflector drum, air flow sieve, 30.5-32 fronts, shedded, 2 owner, combine it has been through IH maint year before last, with 3600 hours, would take 9000 or best offer. I am located 20 miles west from Minn in central S.D. if interested E-mail me I bought newer unit and good luck on the bearing!