It may be cooling internal components that remain warm. Switching off cooking power does not instantly remove stored heat.
What the observation means
The expected duration varies with use and design. A new scraping sound, prolonged unusual running or operation when completely cold deserves a separate enquiry.
A useful next step
Keep required ventilation unobstructed and allow the normal cooldown. Record the preceding load and timing if concerned. Do not insert objects into an opening or isolate and restart repeatedly just to silence the fan, particularly while the appliance is still hot.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.