Things being destroyed on private server when no one is logged in

So I have a private server that I rent and run Minecraft on. Me and two others have access to it only. On two occasions I have logged on to find that some things have been destroyed.

First time I found that several chests had been destroyed and most of my items were scattered on the floor. Today I found that a stair had been destoyed, just as if a creeper had exploded there. And inside my house there had been a few, just two or three, blocks that had been mined away (which caused a huge leak in my inside swimmingpool....)

I'm sure none of the others had anything to do with this, so I'm wondering if the mobs are playing around in my house and messing with my stuff when I'm not around?