DIAGNOSIS The cooling fan is running continuously due to a faulty control relay or a stuck switch, or the transformer is vibrating abnormally.
FIX First, ensure you haven't accidentally activated the 'Vent Fan' function if your model has it (some EM131 variants do). Press the Vent/Exhaust button to turn it off. If the noise stops, that was it.
IF THAT DIDN'T WORK A component on the main control board that controls the fan circuit has failed, sending constant power to the fan. This requires board-level repair or replacement of the main control board.
HEADS UP A continuously running fan will shorten its lifespan. While not an immediate safety issue, it's a sign of an electrical fault that could worsen. Consider unplugging it when not in use.