You must have been on Carnival. Those doors are a BAD design-the balcony doors on other lines SLIDE and so since they slide and are not super heavy like the Carnival doors they do not slam.
Which was my problem- I TRIED not to slam the balcony door but the thing was so heavy and then while out at sea-with the heavy winds-the wind would catch it and SLAM it.
We are booked on Carnival next year-but no balcony for me! I will sleep better in an inside cabin on Carnival.
Now I LOVED the balconies on Celebrity, Princess and Disney! They are GREAT! and their sliding doors are much easier to manuveir when out in the ocean with lots of wind! nothing like Carnival's balcony doors.
BTW-to the OP- even though you were unaware of it I am sure you slammed your door also-I know I did and it did not seem that loud to me when I did it-but I realized from others slamming doors how bad the ocean echoes the noise of shutting your door. what sounded like a small noise to you was magnified about 10 times for your neighbor.
If you don't believe me- just try a balcony on another line and you will be AMAZED how QUIET it is!