took me several visits over few months and 100k pages to solve this intermittent problem, thought i would share what I found . loud grinding from tray 3 only, on (pf740) a 5550ci, would test ok for 100 pages then grind away , changed tires,clutches worked 25k call back more tires+sep clutch went away, 50k noise back, cant make go away, listend with sound meter, comming from drive area took out feed section inspect all drive gears ok, remove rear drive main from lower unit only(pf740) nothing wrong, in-between drive and feed assem (on frame of unit) are three gears screewed in from back, I found one of the shafts not in place no c- clip this allowed it to slide back and forth. this was a factory misstake as we have not serviced this yet, i was able to use paperclip to hold in place, problem solved have photos if any one needs them