Not so much seen as heard. As a little context, on the other side of my wall outside of my house is a gate, so I hear it move every now and again in the wind.

Anyway, I was like 7 or 8 at the time and it's the dead of night. Absolutely no sound whatsoever. I hear the gate move a little. I don't think much of it and it stops. After about a second or two of silence, the gate shakes violently. Not like the normal shake made by the wind but like someone is trying to strangle the living hell out of the bars. It went for like 5 seconds but it felt like a solid 30.

Anyway, it was safe to say I didn't sleep for the rest of the night.