DIAGNOSIS That's the auger motor or a loose mounting bracket hitting the housing. It's a common shipping jostle issue.
FIX Unplug it. Remove the ice basket. Look inside the ice storage area. You'll see the auger assembly. Check if the large white plastic auger itself is seated all the way down. Press firmly. Next, check the four screws securing the motor/bracket assembly to the back wall of the compartment. Tighten them with a Phillips head screwdriver.
IF THAT DIDN'T WORK The noise might be the water pump cavitating. Ensure the unit is perfectly level on the counter. Use a small bubble level. An unlevel machine makes the pump work harder and louder.
HEADS UP Don't ignore this. A persistently loose auger can damage the drive gears. If tightening doesn't stop the knock, contact support. Running it damaged voids the warranty.