Strange noises from locked laundry hut at night looking for logical explanations

Last night around 1am at my house in Osaka, I went to the outdoor toilet. Next to it we have a small laundry hut that is always locked from the inside to keep animals out. It’s winter, so animals don’t usually come around at night.

As I walked past, I heard unusual movement sounds from inside the hut. Loud enough that I stopped to listen. The hut is tightly closed — nothing should be able to enter.

I waited and the sounds continued. My sister heard similar noises a few months ago.

When I opened the door to check, everything immediately stopped — and there was nothing inside.

Has anyone experienced something similar or have a logical explanation?