The main noise problems from the HP 4000 LaserJet printers comes from the MP tray clutch assembly, which sounds like a gear moving roughly inside the front of the machine. Typically, by opening the MP tray door, you can hold onto the feed roller and feel it. By gently moving the feed roller slightly in one direction or another you can change the noise. If the noise is really bad you can even watch the feed roller rattle in place. Remove the MP pick up assembly, disassemble the clutch, clean it out, lubricate it slightly, then reinstall. Or just slightly spray some oil into the pick up assembly without removal, but it is generally preferred to take it out and rebuild it to make sure it doesn't happen again.

Another noise problem is a loud clicking noise when MP tray picks up the paper, which is caused by the pick up solenoid. Again, the only thing you can do there is replace the solenoid pick up assembly (part# RH7-2672) or refurbish the solenoid if you can find a suitable material to replace the worn dampener.

Squeaks usually come in two places. The first is the transfer roller. Originally, the metal shafts on either end were not lubricated. Over time they start to squeak. Remove the transfer roller, clean the shafts, and apply a little lubrication. Grease should be used here as oil will drift into the roller and get absorbed causing imaging problems on the sides. Most new transfer rollers, especially in the 4200 series, have grease on them; a nice, black grease that tends to get on your hands and everything you touch for the next five minutes!

The second squeak I hear a lot comes from the exit roller shaft. Sitting on top of the shaft is two black guides.

Remove the top cover and top of the exit assembly, then remove the guides and place a drop of oil were the guides come into contact with the metal shaft. Grease is too thick here. Placing grease on the shaft will cause the guides to want to move up when the machine is running causing a rattling noise.