it makes a loud grinding or squealing noise from the right side when it starts up or prints

Diagnosis

The loud grinding or high-pitched squealing emanating from the right side of the HP LaserJet Pro M404dn is almost always caused by a mechanical failure within the fuser assembly, specifically the drive gear assembly or the pressure roller bearings. When the printer initializes or begins a print job, the fuser motor engages to heat and rotate the rollers. If the plastic teeth on the drive gear have stripped or if the internal lubricant has dried out and hardened, the gears will slip or "chatter," creating a rhythmic grinding sound. In cases where the noise is more of a piercing squeal, the issue is typically a seized bearing in the fuser's pressure roller. This happens when toner dust and paper fibers infiltrate the bearing housing, increasing friction to the point where the motor struggles to rotate the roller at the required RPM. You can confirm this by opening the rear door and observing the fuser rollers; if you see uneven wear patterns or "flat spots" on the orange/black rollers, the internal mechanical drive is failing. If the noise persists even when the toner cartridge is removed, the fault is isolated to the fuser or the main drive motor assembly on the right chassis.

How to Fix It

To resolve this, you must replace the fuser assembly. For the M404dn, you will need the HP Fuser Assembly (Part Number: RM2-4458 or the updated equivalent for the M400 series). Follow these exact steps for a clean installation:

1. Power down the printer completely and disconnect the AC power cord from the wall. Wait at least 30 minutes for the fuser to cool down to avoid severe burns.
2. Open the front toner access door and remove the HP 58A/X toner cartridge to clear the path and prevent any accidental spills.
3. Navigate to the rear of the printer and open the rear output door by pulling the two release tabs located on the left and right edges of the rear panel.
4. Locate the two blue fuser release levers. These are spring-loaded tabs that lock the fuser into the drive gear assembly. Pull both levers outward simultaneously to disengage the locking mechanism.
5. Grasp the fuser assembly by the designated handles and slide the unit straight out toward the rear of the machine. Do not tilt the unit, as this can damage the remaining drive gears in the chassis.
6. Slide the new RM2-4458 fuser assembly into the slot, ensuring the drive gear on the right side aligns perfectly with the printer's drive motor.
7. Push the fuser in firmly until you hear a click, then snap the blue release levers back into their locked positions.
8. Close the rear door, reinsert the toner cartridge, close the front door, and reconnect the power.

If That Didn't Work

• Check the Pickup Roller Assembly: If the noise only occurs the moment the paper starts to move (before it reaches the fuser), the pickup roller gear may be stripped. Inspect the gear on the right side of the paper tray lift mechanism for missing teeth or white plastic shavings.
• Inspect the Transfer Roller: A worn transfer roller (the spongy roller under the toner cartridge) can sometimes cause a rubbing noise. Remove the toner and check if the roller rotates freely by hand. If it feels "stuck" or makes a clicking sound, replace the transfer roller assembly.
• Main Drive Motor Replacement: If the grinding sound is coming from deep within the right-side chassis and the fuser replacement didn't stop it, the main drive motor (Part: RM2-4444) may have a failed bearing. This requires a full teardown of the right-side plastic casing to access and replace the motor.
• Clean the Paper Path: Occasionally, a small piece of torn paper or a foreign object (like a staple) can get lodged in the right-side duplexing gear. Use a flashlight to inspect the area behind the fuser for debris that could be causing mechanical interference.

Heads Up

• Burn Hazard: The fuser operates at temperatures exceeding 200°C. Never attempt to touch the rollers or remove the assembly immediately after printing.
• Avoid Lubricants: Never apply WD-40 or generic grease to the fuser gears. The high heat will cause these lubricants to melt and leak onto the paper, causing permanent streaks and smears.
• Gear Alignment: When inserting the new fuser, ensure it is seated perfectly flush. If it is slightly skewed, the gears will strip within the first 100 pages of printing.
• Toner Compatibility: Using low-quality third-party toner can lead to "toner buildup" on the fuser rollers, which increases the mechanical load on the gears and accelerates wear.