Some designs alter fan operation with door position, so the change is useful evidence. It does not establish whether ice, a loose fitting or a fan fault is responsible.
What the observation tells you
Do not hold the door sensor closed or remove a cover to watch moving parts. A scraping sound should not be repeatedly recreated while food warms. Note any visible frost near an outlet without probing it.
A useful next step
Report the normal door-open and door-closed difference, the onset and the temperature condition. Use the prescribed food-protection plan while an unusual persistent sound is assessed.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.