Hey Guys,
When I would like to at the object from an certainly direction, I can see the lines, even though I turned off the overlay. Is this only a show error or did I something wrong.
Thank you 
It looks like you have some z-fighting there, especially in the lighter part of the mesh. You likely have a duplicate mesh identical to the other, causing the object to look weird as multiple faces are perfectly aligned with each other. I am not sure about the other faint lines in the brown section, but it also could possibly be caused by that.
Thank you I´ve read me a bit trough the z-fighting, I didn´t know that this error has a name. Great article. Thanks!!