Hi, I have had similar problems with this flickering or z fighting when I have been creating buildings.
I have a fix which i hope should help:

First test this on a copy of your model, not an original.

1. Place each element on a separate layer ie, terrain, building - nothing should be left on layer 0. If you have one element that flickers just place it on a layer called layer 1.
2. Explode all surfaces until they explode no further
3. Each layer in turn needs re-grouping, do this for all layers
4. Select each layer in turn right click group and select soften smooth edges/soften coplanar - Tick both boxes and leave 20 as the default smoothing level.
5. Once done go to view>hidden geometry and again view>edges (make edges unticked or off)
6. Road test by orbiting the flickering should be gone.