I couldn't find anything about a problem i had with Railclone flickering so I am writing about my findings to help others. I had a problem where geometry appeared to be tearing at render time. After tons of digging I could find nothing anywhere about my issue.. train tracks appears to have overlapping and flickering faces for no reason. Mirror COULD be one culprit with rail clone, that that was off. VRay and render settings could be a culprit too, but they were all good to go.
Eventually I notice the object had a strange scale of 150,150,100... but with Railclone scale is irrelevant because the object creates itself dynamically anyway, so both location and scale *shouldn't matter.... but it does. So I zeroed out the transforms, and set scale to 100,100,100 and it fixed the flickering in my rendering. And it only took me 3 days to figure this out.
So apparently what happens is that it creates and tries to scale the object at the same time, creating random irrational pops and flashes. So yeah, if you are having this issue.. check your transforms! Now buy me a pizza if this helps you.