Some faces are not 'flat' or 'coplanar'. So they are intersecting with other faces. Switch the view to Xray mode to see what I mean. If you expect this to happen [but I think NOT!] and want edges at show at those intersections, then select a face ad right-click context-menu intersect... Model all geometry on 'Layer0' [always have that set as the active layer] To keep the modeling neat and tidy make groups of related geometry. That way grouped parts don't 'stick together' and you can even assign a new layer to them, which you can switch off, controlling visibility and making working with multi-level projects much easier...