There are lots of Sonar automation videos on Youtube, e.g.
here . Fading the volume of the track with the effect inserted will fade the noise as sharke says.
However, if you're after an authentic vinyl effect, I guess you shouldn't apply the fade to the vinyl noise. If you were listening to a record, the fade would only affect the music, then the needle would lift off (making a different noise), stopping the noise rather than fading it.