Low "warning" sound when driver seat door opens and closes

[Cujo]

Recently I have experienced that my Enyaq gives a low warning sound when opening and closing the driver seat door. If I reopen and close the door again, it doesn't give the sound again. It has not be consistently at all, but just happened a few times over that last couple of days. I cannot figure out what would be the cause of the warning (or if it is a warning at all), since there is no other indications of a problem.

Anyone had any similar experiences?