I was suffering from distance fog flickering on and off repeatedly in MTA DM but not normal GTASA, I found the solution after a bit of searching, so I figured I would post it here in case any of you suffere from in in the future.
Firstly it seems to be an ATI only problem.
I found the answer here
http://forum.mtasa.com/viewtopic.php?f=95&t=21161&p=267860&hilit=ati#p267860
basically all i had to do was type "ceguitext 1" in the console, apparently this code changes Chat and Nickname text but also has the side effect of fixing the fog flicker on ati cards
enjoy!!!