Trampoline Visitor?

This happened when I was about 15 or 16 years old. I had a trampoline in my back yard which was fenced in by a chain metal fence.

My cousin & I were laying in my bed, talking, about to fall asleep when we heard what sounded like someone jumping on my trampoline. We both stopped talking & I sat up, wanting to look out my window to see what was out there. As I was doing so, the sound stopped completely. My window had been open. I recall this, because I always to this day, sleep with a window open. If anyone would have been out there, we would have heard them jump the fence! My window looked right out to the backyard & the fence began right next to it also, we would have definitely heard someone jump it.

We both tried to go to sleep when we heard it again. I this time, only remember falling asleep. Maybe it was an Alien, thinking he was on the Moon?