I work at a school from 3 to 11:30pm.

After the last guy (excluding myself) leaves at 10pm, weird things happen. Doors slam suddenly and voices like people talking 50ft away from where I am.
It doesn 't matter the area. Sometimes I will run towards the spot from where the noise came, but nothing is seen or heard once there.
This holy week we worked earlier and my pal left at 9pm (but he didn 't let me know). At 9:50pm someone was moving chairs and tables at the gym, and slammed the doors. I went to check, calling my pal and nobody replied. I called him on the phone and he was already at home.
If anybody has the same experience , please comment.