Diagnosis
The drive coupler, which connects the motor to the blade assembly, is likely worn or damaged. This is a common wear component.
How to Fix It
Remove the jar from the base. Inspect the black plastic drive socket on the bottom of the jar. Look for cracked, rounded-off, or missing splines inside the socket. A damaged drive socket requires jar replacement.
If That Didn't Work
Examine the metal drive coupler pin protruding from the blender base. Ensure it is not bent, broken, or covered in debris. Wipe it clean with a dry cloth.
Heads Up
This noise is often caused by using the tamper excessively on high-speed settings, which overloads the coupler. Use the tamper only on speeds 1-4 for thick mixtures.