A loose accessory can vibrate, but sound alone cannot establish the source. Distinguish an accessory rattle from scraping, grinding or other abnormal mechanical noise.
What the observation means
When the oven is fully cool, check only that permitted shelves and trays are seated as the manual shows. Do not touch or reach through a fan cover. A sound that begins after loading an unfamiliar tray gives different context from one present with the normal arrangement.
A useful next step
Record when the noise appears and which accessories were fitted. If the sound is harsh or accompanies a heating problem, leave the oven unused for assessment. Do not run it with protective covers removed to locate the noise.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.