This story will be a short one, it happened to me and friends when we were living in the school dorm. Just to give you an idea of how our dorm room looks like; imagine a square, each corner has a semi-bunk bed (similar to a bunk bed, but instead of two beds, below are a desk and a dresser), and the front door is located in between the two semi-bunk beds on the right, bathroom is located opposite of the room. Now you have a sense of where everything is, here goes the story,
I used to live in my school hostel with three of my closest friends. We usually went to bed at around 12am, and my friend, Dia, whose bed located on the right side of the front door (which is also beside the light switch), would always turn off the lights after seeing everyone well-tucked in their beds. One night, as we all climbed up to our warm beds, Dia turned off the lights and we were all ready to have a good night sleep. A few minutes after the lights were off, we heard heavy footsteps running at the corridor outside of our room. This running footsteps occurred quite often, it was more active during the night. We laughed it off as we were kind of used to the odd noises in the dorm.
As we went back to sleep, "BANG BANG BANG", someone was knocking heavily on our door. We were annoyed, especially Dia as her bed was just beside the door. "BANG BANG BANG", the second time was loud enough to sit us all up, we were puzzled and annoyed by the fact that it is already midnight, why would anyone be knocking on our door at this hour? Annoyed, Dia shouted, "Who is it?", no response. She reached down to unlocked the door and push the door open. As the door flung wide open, there was nobody outside there, she peeked her head outside and scanned the corridor, there was literally no one. She quickly closed the door. All of us sat in silence for awhile. We looked at each other (with the light source from our phones) and finally Mei asked, "who was that", to which Dia responded, "there was no one, let's just go back to bed.". Everyone knew something was not right, but we did not want to make a big fuss about it. So we went back to sleep, nothing really happened the next day or days after, we figured someone or something might have played a trick on us, or it simply just want to come in.
Last year, similar thing happened to my sister in Taiwan when she was staying in her Uni dorm. It was around the Hungry Ghost Month, she was resting in her room with two of her roommates. This happened at around 8-9pm, as she was doing her night time face routine, she heard three knocks on the door. Without any hesitation, she stood up and went to open the door, only to her shock, nobody was there. She looked around the corridor, no one was around. Puzzled, she went back to her desk and asked her roommate if they heard the knocking too. To her surprised, only one of them heard it, the other one was confused why she suddenly stood up and open the door. Apparently, the same thing happened to one of their friends who lived in the opposite block, for some reason, some heard the knocks, some didn't.