DIAGNOSIS This model has an automatic fan feature tied to humidity. If it senses high moisture from cooking (like boiling pasta), it'll kick on the vent fan to help clear the air, and it can be stubborn to turn off manually.
FIX Look for the 'Fan Auto On' or 'Auto Fan' button on your control panel. Press it once to turn the feature off. The fan should stop within a few minutes as the humidity level drops. If you don't see that specific button, press the 'Fan Speed' button repeatedly until it cycles to 'Off'.
IF THAT DIDN'T WORK It's possible the humidity sensor behind the front grille is dirty or malfunctioning, making it overly sensitive. Unplug the microwave and wipe the small sensor vent (it looks like a little grid or hole) with a dry cloth to remove any grease or dust.
HEADS UP The fan running automatically is a feature, not a bug, but it can be annoying. If you disable 'Auto Fan', remember you'll need to manually turn on the vent for smoky or steamy cooking.