grinder on my dgb-900bc is making a loud screeching or rattling noise but won't actually grind the beans.

Diagnosis

The loud screeching or rattling noise in your Cuisinart DGB-900BC is caused by a mechanical failure in the gear train, specifically the nylon drive gears that connect the motor to the grinding burrs. When the motor spins but the beans aren't being processed, it indicates that the teeth on the primary drive gear have stripped or the gear has cracked, causing it to slip against the secondary gear. This creates a high-pitched friction sound (the screech) or a rhythmic clattering (the rattle) as the motor spins freely without engaging the burr. This failure typically occurs due to "bean jamming," where a particularly hard coffee bean or a foreign object (like a small pebble often found in bulk beans) wedges into the burrs. Because the motor is powerful, it continues to push, and the nylon gear—designed as a "sacrificial" part to prevent the motor from burning out—shears its teeth. You can confirm this by attempting to rotate the grinding burr manually (with the unit unplugged); if the burr spins loosely or feels disconnected from the motor's resistance, the gear train is compromised.

How to Fix It

Since the internal nylon gears are molded into the assembly and cannot be replaced individually, you must replace the entire Grinder Housing Assembly (Part No. SP-357190).

1. Unplug the machine and remove the water reservoir and the coffee carafe.
2. Remove the bean hopper by unscrewing the retaining screws located on the underside of the hopper assembly.
3. Flip the machine on its side. You will see the motor housing bolted to the chassis. Remove the four T15 Torx screws securing the grinder motor assembly to the main frame.
4. Carefully disconnect the wiring harness. Press the small plastic tab on the connector and pull the plug away from the main control board.
5. Lift the damaged grinder assembly out of the chassis. Note the orientation of the drive shaft to ensure the new part aligns perfectly with the brew basket chute.
6. Insert the new SP-357190 assembly, ensuring the alignment pins seat firmly into the chassis slots.
7. Reconnect the wiring harness until you hear a distinct click.
8. Reinstall the four T15 Torx screws, tightening them in a cross-pattern to avoid warping the plastic housing.
9. Reattach the bean hopper and run a "Grind Only" cycle with a small amount of beans to verify the burrs are engaging properly.

If That Didn't Work

• Check for Obstructions in the Chute: If the new assembly still makes noise, a fragment of the old broken gear may be lodged in the chute leading to the filter basket. Use a vacuum or a long pipe cleaner to clear the path from the grinder output to the brew basket.
• Inspect the Motor Capacitor: If the motor hums but doesn't spin the gears, the start capacitor may have failed. This is a separate electrical component located near the base. If the capacitor is bulged or leaking, it must be replaced to provide the initial torque needed to turn the burrs.
• Verify the Control Board Relay: If the grinder intermittently fails to engage despite a new assembly, the relay on the main PCB may be pitted. Inspect the board for charred areas or "cold" solder joints near the grinder power lead.
• Recalibrate the Burr Gap: If the noise is a grinding sound rather than a screech, the burrs may be touching. Adjust the grind setting to a coarser level to see if the noise subsides, as overly fine settings can put excessive strain on the nylon gears.

Heads Up

• Avoid using "dark roast" beans that are excessively oily; the oil can build up as a sticky residue in the gear housing, increasing friction and accelerating gear wear.
• Never use a vacuum cleaner to suck beans out of the hopper while the machine is plugged in, as this can trigger a sensor error or cause the motor to spin backward.
• Periodically clean the burrs using a dedicated grinder cleaning tablet or a small brush to remove "fines" that accumulate and create resistance.
• If you hear a sudden change in pitch during grinding, stop the machine immediately. Continuing to run the motor while the burrs are jammed is what causes the nylon gears to strip.