My Three Unexplainable Ghost Experiences

I'm 17 years old. Two of these stories take place in my hometown, Duluth. One of them even occurred in my current town, a suburb of Minneapolis at my house. I've always believed in the supernatural, especially after these experiences. Enough with the introduction, on to the stories.

I used to have a friend that doesn't believe in anything she can't see, and she couldn't come up with any explanation other than "I made them up." Which I didn't, but whatever makes her happy, I guess. They both occurred in my house that I grew up most of my life in, in Duluth. Actually, there's also a third one that happened that was in my current house. In my Duluth house, I was sitting at my desk, talking to my best online friend on a chat room. I was around 12 or 13 at the time. I had a glass dolphin on my desk right beside me that I got not too long ago at the time. So, as I was typing a message, out of the corner of my eye, I saw the back end of the dolphin get lifted up. I didn't react because I thought my mind was playing tricks on me, but then the back end of the dolphin slammed against the desk making this loud shattering/banging noise. I jumped and screamed, and the tail of my dolphin was gone. I actually still have this dolphin, but I don't know where it is at the moment. I wish I did so I could include the picture.

Second story, I was definitely 13 during this story. I was in the process of moving to where I currently am. My house was pretty empty at the time. I was hanging out with my best friend and I saw her knocking on the wall. I asked her what she was doing and she told me that she heard someone knocking back. I approached the wall and I heard light knocking, and then my best friend knocked louder on the door and we both kind of backed away from the door. After we both were obviously away from the wall, he heard a loud BANG. The creepiest part is something could've easily been behind that wall, the other side of the wall was a storage area underneath my stairs.

Last and third story, this is after I moved. I was dancing in my bedroom to some music, and then I hit what felt like a wall. I froze and turned around, there was about a person length between me and the wall. I'm still wondering what the heck with those experiences.