An Unknown Knocker

From: 
Story type: Ghost
Location: my front door
Source: Form Submission

One day My mom, sister and I were comming back home from a friends house. We got home and right when my mom was about to unlock the front door, we all heard a knock coming from inside the door close to the bottom of the door. we all freaked out, We opened the door and there was nothing we only heard little footsteps running down the hallway.