All I can think of is that it is meant to confirm intercom request or confirm button push, but ding dong isn't appropriate. It's like if you heard your ringtone every time you send a text.I will be willing to test it. I cannot see having a loud audible ding dong on the outside of the door makes any sense. Is there a reason for it?
It's so ridiculous that people walking on the other side of the street turn their heads to see what the hell is making that sound .