DIAGNOSIS Something hard—like a pit, a seed, or a piece of ice—has gotten wedged against the blades or the bearing, or the blade assembly's plastic gears are stripping.
FIX Stop using it immediately. Unplug it. Unscrew the cup and inspect the blade assembly. Look for any foreign object stuck between a blade and the plastic housing. Remove it. Spin the blades by hand (carefully!). If they grind or feel gritty, the bearing inside the blade unit is likely damaged.
IF THAT DIDN'T WORK If no debris is visible and the blades spin smoothly by hand, the issue might be in the motor base's drive socket. Look inside the base where the blade unit attaches. If you see broken plastic teeth, the base is damaged.
HEADS UP Always check for and remove peach pits, mango seeds, large strawberry stems, etc., before blending. These can destroy the blades or the motor. The motor isn't strong enough to chop through them.