it's making a really loud grinding noise only on the higher speed settings, sounds awful compared to my old blender.

Diagnosis

The grinding noise occurring specifically at high RPMs on the Blendtec Designer 650 is typically caused by a failure of the drive socket (the plastic coupler) or a misalignment between the motor drive pin and the jar base. At low speeds, the torque is low enough that the components may still grip, but as the motor ramps up to its maximum speed, any slight rounding of the internal plastic splines causes the drive pin to "chatter" or slip against the socket walls. This creates a high-frequency metallic grinding sound that can be mistaken for motor failure. Another possibility is the degradation of the blade bearing assembly within the jar. If the bearing has developed a flat spot or has ingested moisture/fine powder, it will hum at low speeds but scream or grind once it hits the high-velocity centrifugal force of the Designer 650's motor. You can confirm this by removing the jar and spinning the blade manually with a tool; if you feel any "grit" or resistance during the rotation, the bearing is shot. If the blade spins smoothly by hand, the issue is almost certainly the drive socket interface.

How to Fix It

To resolve a drive socket failure, you must replace the worn plastic interface. Unlike some blenders, the Blendtec Designer 650 uses a socket integrated into the jar base, meaning you are often replacing the jar or the base assembly depending on the specific model year.

1. Unplug the blender from the wall outlet to ensure no accidental activation occurs.
2. Lift the jar straight up and off the motor base.
3. Turn the jar upside down and inspect the black plastic drive socket located in the center of the base.
4. Insert a small flashlight into the socket. Look for "rounding"—where the sharp edges of the internal splines have become smooth or melted. Check for any black plastic shavings or "dust" around the rim of the socket.
5. If the socket is worn, remove the jar entirely. If you have a replacement jar, seat it firmly onto the base, ensuring it is perfectly vertical.
6. If replacing only the socket (on compatible models), use a flat-head screwdriver to gently pry the old socket out of the base housing.
7. Press the new drive socket firmly into the housing until it clicks or seats flush.
8. Place the jar back on the base and perform a "dry test" by pulsing the blender for 1 second to ensure the grinding noise has ceased before adding ingredients.

If That Didn't Work

• Inspect the Motor Drive Pin: Look at the metal pin protruding from the motor base. If the pin is bent even by a fraction of a millimeter, it will not enter the socket squarely, causing a grinding noise at high speeds. Use a square tool to check for alignment. If bent, the motor base assembly must be serviced.
• Check for Jar Base Warping: Place the jar on a completely flat surface (like a granite countertop). If the jar wobbles, the base is warped. This causes the drive pin to enter the socket at an angle, creating friction and noise at high RPMs. You will need to replace the jar.
• Clear Debris from the Drive Cavity: Sometimes a small piece of hard food or a seed gets trapped in the gap between the jar base and the motor housing. Use compressed air to blow out the drive area of the motor base to ensure there is no foreign object causing the vibration.
• Bearing Failure: If the noise persists and the socket is pristine, the internal blade bearing has failed. This is a non-serviceable part of the Blendtec jar. You will need to replace the entire jar assembly to restore silent operation.

Heads Up

• Avoid "dry running" the blender at high speeds for extended periods, as this generates heat that can melt the plastic drive socket.
• Never use metal utensils to stir ingredients while the jar is on the base; if the blade is slightly bent, it will cause catastrophic grinding noise at high speeds.
• When seating the jar, always ensure it is pushed down firmly. A "floating" jar will strip the drive socket in seconds.
• Periodically wipe the motor drive pin with a damp cloth to remove leaked liquids, which can attract grit and accelerate the wear of the plastic coupler.