What would cause this?
Are you using a non-standard camera, like Chaseplane ? If yes, you might want to check its settings, because flickering in the distance is usually caused by a camera minimum clip plane too small, which has been made that way to be able to go very close to some objects without them being clipped but, the downside of it, is that objects far away will flicker because of the limited precision of the z-buffer of the graphic card, which cannot work well with very close and very far objects at the same time.
