So I have a simple scene in blender, there is a track situaded in a grass field. However it seems that the road somehow inteferes with the plane. If I (re)move the track it solves the problem. The same happens with a little car I have that isn't shown. The grass texture is a seamless grass texture 1024x1024 if I recall correctly.
I've chequed the bounding boxes and wireframes and everything seems good. You can download the .blend file below.



