graphical glitch: black strings reaching in to the sky

[The_Watcher]

Hi there,
I recently built a new machine and have FAF installed.
I've played a few skirmishes and keep encountering, at random, strange graphical glitches.
Specifically, buildings and/or trees will have "strings" or "lines" reaching from the ground up, infinitely, in to the sky. These strings also cast a shadow across the landscape.
I've searched the forums and haven't found anything relevant just yet.

Has anyone else encountered this before, and fixed it?
Many thanks