DIAGNOSIS: The plastic drive coupler that engages the ice-crush mechanism is worn down or cracked. The K150 uses a specific internal gear train for the pulse/ice crush function.
FIX: This is a base/motor unit issue. Stop using the ice crush setting immediately to prevent further damage. The grinding is metal or plastic gears stripping. For the K150, repairing this internal gearbox is not a typical DIY job. You must contact KitchenAid for service or a base replacement.
IF THAT DIDN'T WORK: If the noise seems to come more from the jar, ensure you're using the ice crush function correctly: add enough liquid, use the "Pulse" button in short bursts, and don't overload with solid ice. Continuous grinding on that setting with proper technique confirms the internal fault.
HEADS UP: The ice crush setting is a high-torque, pulsed function. Never hold the button down for more than 5-7 seconds. Always use a combination of pulse bursts and pauses to process ice.