Diagnosis
The grinding noise indicates severe mechanical failure inside the motor housing. This is most commonly due to damaged or seized motor bearings or stripped plastic drive gears connecting the motor to the blade shaft. The acrid burning smell confirms the electric motor is overheating, which is likely burning the insulation on its internal windings due to the excessive friction and load.
How to Fix It
Immediately unplug the blender and do not use it again. For the KHBV53 model, the motor unit is not user-serviceable. Your only safe options are to contact KitchenAid customer service for warranty assessment or to seek a professional small appliance repair shop that can disassemble the sealed housing, diagnose the exact failed component (motor or gears), and source a replacement part. Attempting a DIY fix risks electric shock and will likely void any remaining warranty.
If That Didn't Work
If professional repair is not cost-effective, the entire hand blender unit must be replaced. Continued operation is not an option; it will lead to a complete motor burnout, pose a significant fire hazard, and could cause the unit to seize or shed metal fragments into your food.
Heads Up
This failure is frequently caused by applying too much sideways pressure, like forcing the blade assembly against the bottom or hard sides of a container, which bends the shaft and ruins the bearings. Always keep the blender moving and let the sharp blades pull food into the vortex naturally.