Have you fully enclosed your Taz to trap in heat and prevent cross drafts from cooling part as it prints?
Is your part warping up off of the bed during the printing process? Perhaps not enough ABS/acetone juice?
I have raised my bed temp to 95 degrees, and the people at the shop where we bought our TAZ usually print ABS at 105-110.
I saw this same type of chatter once. That was before we enclosed the printer and raised the bed temp.
I think blasts of cool air during the printing process caused my issues with chatter. People walking up to the printer to watch it print and being in a drafty location.
Also - are you printing with the fan on? For larger flat parts like that I make sure the cooling fan never runs.