Some models have characteristic switching or mechanical sounds, but the manual and the appliance's established behaviour are the relevant comparison. A newly loud impact should not be dismissed as a normal start-up feature.
What the observation tells you
Note whether the sound happens once at the control, comes from the chamber or continues during operation. Do not lean into the opening or repeat starts to locate it. A recent dropped object or changed accessory is important history.
A useful next step
If the sound is new or accompanied by poor grinding, movement or leakage, stop use and arrange assessment. Keep a safe-distance recording if one was already made.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.