OK so a little back story...
About two years ago at this point I was at my friends house. For privacy sake, we'll call him Kevin. Kevin has a pretty nice brick house in the middle of town. So we got a bit bored and we decided to go into the basement. So at this basement there are two rooms, one has the room to the under house where it's just a bunch of dirt and pillars. Then there's the water heater, bows, and then a huge heavy punching bag hanging on the ceiling. I'm the other room, there's a couch, a plasma TV, exercising tools, and a cabinet full of Nerf guns. So he showed his compound bow (side note: it was a nice bow) and as we left the room, I gently and playfully pushed the punching bag and then Kevin stopped it.  Afterwards he decided to show some Nerf guns. That is when things got creepy.  We heard a peculiar noise. "Creak,Creak,Creak"
It took us was while to brave up. When we checked, the over 100lb punching bag was swinging.  We bolted. I was into contact with Kevin, and he said the bag has never made that noise again. He said that why he bolted was he saw a shadow figure come out from the door.  Sad thing was, there was no recordings....