I have the same exact error message and the printer is doing the same thing. What is happening is that as long as tray 2 is in the printer will lift the paper in the tray. Yes the tab is moving. The printer does not realize that the paper is at the top and keeps on trying to lift the paper some more. When tray 2 is removed the noise stops. Printing from tray 1 is fine. I am glad to see that someone else had this problem and I was actually under the impression that the flag or sensor for the flag is not working. Especially after seeing the parts that were replaced did not solve the problem. I have heard this same noise coming from an HP Laserjet 5SI out of tray 4. Once that tray is set up for plain paper it looks to some like you can store paper on the left side. But with paper stored there it will not allow the tray to lift. Which then causes the thumping noise. Hope someone has some info for me. If I could find a manual on line that would really help. If any one can tell me where to get it I would appreciate it.