DIAGNOSIS That grinding is usually the sound of the evaporator plate—the cold metal part that freezes the water—scraping against ice that didn't fully eject or a piece of mineral deposit.
FIX Turn the unit off and unplug it. Open the top and look at the silver evaporator plate (the grid where the ice forms). You'll likely see a partial ice cube or a chunk of ice stuck to it. Let it melt completely (you can pour a little warm water over it, NOT hot). Once clear, dry it off, plug it back in, and restart. The noise should be gone.
IF THAT DIDN'T WORK If the noise persists after clearing obvious ice, you might have a piece of plastic packaging or a small foreign object that got into the works during assembly. You'll need to inspect the area around the evaporator and the fan at the back.
HEADS UP Never use a knife or metal tool to chip ice off the evaporator plate. You'll puncture it and ruin the machine. Patience and warm water only.