If you're playing back videotape with VITC burned in, it will output with the video regardless of whether the machine is told it should use it or not. What you need is to blank the lines associated with VITC, or tell the Avid to ignore it. To blank the lines at the machine, go to Setup, VTR Setup, and in there will be a setting called Blank Line. It is normally set to "All Through" which will pass the lines through to the machine's outs. You can either select the VITC lines to be blanked or choose "All Blank" and it should cover over those data lines with video black on output.