My computer have problems so it took a while for me to answer, this is a picture of an other computer with clean install of unreal engine 4.7.3, using the base cube that comes with the engine with no blueprint :
As you can see, the problem is a lot less noticeable, but still there.
You need to fly far enough from the cubes and then you will try to see these little artifacts.
I just want it to look like a seamless floor.