I think my house is haunted

Yesterday early in the day my cat was chasing a bug around my office. I went outside to water some flowers and vegetables and when I came back in I didn't see him.

As I sat here writing I kept hearing what sounded like human footsteps upstairs. It got my attention enough that I looked outside to make sure my sisters car wasn't in the driveway, thinking maybe she came home early when I was outside and I didn't notice. No car.

At that point I gave up and figured I was just imagining things. Until my son came home from school. He asked me why I locked the cat in the basement. I said I didn't, and to make my point I got up and checked the basement door. It was open. I called out "Cat!" down the basement stairs, nothing. He almost always answers me. My son said he heard the cat meowing somewhere. I checked my bedroom downstairs. No cat. I checked the downstairs bathroom. No cat.

I went upstairs and yelled "Cat!" and heard a response this time. I figured maybe he got into the attic again via my sister's closet because she seems to leave her door cracked open and her closet door open so he can get to the access panel and push it in. But when I went in her room and called for him the response was not coming from that direction.

Stumped, I checked my sons room, which also had the door left cracked open. No cat. I checked the bathroom. No cat. The other two doors up there were closed. Those two doors are always closed as I insist on it. They are the doors to my stepsons rooms, and they are total slobs. I don't want my son or sister bringing a friend home and seeing in there.

I stood in the middle of the hallway and called out to the cat again. The response sounded like it was coming from my oldest stepsons room. I opened the door and sure enough, the cat ran out, all freaked out looking with his pupils wide open. Very strange. :/