Cancelling cooking does not immediately remove stored heat. A cooling system may continue while components return towards their normal temperature.
What the observation means
The relevant distinction is between a purposeful cooldown and a new prolonged or abnormal noise. Do not cut ventilation simply because the heating selection is Off. A separate cooking fan may have a different role from the cooling fan.
A useful next step
Allow the normal process described in the manual. If the sound continues unusually long, becomes harsh or occurs when the appliance has been cold for a long period, record that pattern for assessment. Do not reach through vents or interrupt power repeatedly as a test.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.