Looks like a sparks texture stretched out and gone wrong, doesn't it? Hmm. Maybe it was induced by the skinpack you're running on those cars? Does the issue still occur with the stock 80s Formula Classic? I'f all else fails, verifying integrity of original files on Steam would be a good strategy -- that should revert whatever has changed. This weird sparkles behaviour is not anything I've seen in my AMS install, that's for sure.