What happened? Paranormal activity? Please answer.?

Ok so me and my friend where sitting in her room and I was recording her singing on garage band. There was nothing weird on the recording but after we stopped recording the blinds flew out and then smashed into the wndow. There was no one near it and nothing bumped it were sure. There was no earthquake the window was shut tight because we checked right after we finished freaking out. We thought of any logical explination and no one who is in the house right now can think of one either besides ghosts or something. There have been weird things happening in her house before and mine witch is right across the street.