Different door sensors can affect different fans or functions. Noting the response during ordinary opening helps localise the behaviour without exposing moving parts.
What the observation tells you
A sound stopping with one door but not the other is more precise than 'it stops when opened'. It does not prove the fan itself is defective; ice or another condition may be involved. Do not hold sensors or magnets in place to recreate operation.
A useful next step
Make a brief safe observation and record any cooling or frost change. Leave panels closed and seek assessment for a persistent new scrape or vibration.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.