I have a Hewlett Packard Laserjet 4L printer. Very reliable printer. This one was hardly used when I got it about 3 years ago. I worked on the solenoids, to repair a problem typical of printers this age, soon after I got it. Since then, no problems, until now.
Last week I replaced the toner cartridge with a remanufactured one. It didn't seem to fit well. Then the top door didn't close well. And today it stopped printing. Instead, it makes a high frequency grinding/humming noise. It does not even attempt to draw any paper. It will make this noise even if the paper tray is empty. It sounds like a gear is slipping, maybe.