Aircraft trailing smoke to ground

Hello:I know I have seen this somewhere, but a search hasn't helped me. I noticed recently that on approach(during replay) that my aircraft are trailing what looks like smoke straight down toward the ground and even when on the ground. This is not the same as the snow effect that FS has during the winter in the north. I just started using FSX again recently after putting in more RAM so I don't remember when it started. Like I said above, I have seen this on the forums before but, I don't know if it was here or on the FS9 forum. Either way, a search of the forums got me nothing.Does anyone remember what the fix is for this?Thanks RichardS