I have a 1979 TR70 with ~4600 hours on it. I rebuilt the feederhouse at ~4000 hours with a new chain and all new bearings. Last year while doing corn it started making a noise from what sounds like where the feederhouse and the separator meet. It sounds like it is crushing gravel any time there is material flowing into the machine. You stop feeding material in, the sound goes away. When you are outside the machine or have the window open you can’t hear it. I took the slip clutch on the feederhouse apart and the piece the springs push on was cracked so I put a new one of those in, readjusted the springs to the book specs and it still does it. The feederhouse chain is tight and I am at a complete loss of what else it could be. Thought maybe collectively you might have had this experience, know something I am over looking. This is the machines last year on my farm, only have 30 acres of beans left to go, but I don’t want to sell someone something broken, and I don’t want to be stranded.