Hi my name isXXXXX have been an appliance service tech since 1992. Let me pull the model number up and will be back.
One of your limit switches is stuck. This would cause your Vent to come up and down on its own.Part# XXXXX Other than shutting off your breaker there is nothing you can do to stop it from happening. Do you want to attempt to repair on your own i can send you some details on how to?
Send me some details on how I can attempt to fix it myself. Thanks