The noise in this case I believe is coming from the AA not being high enough, not the AO.
Go into the render settings, then quality, then turn up your unified sampling quality to around 1 and try again.
I hope you're enjoying the tutorial thus far 
All the best
Dave
From a readers' Q and A column in TV GUIDE: "If we get involved in a nuclear war, would the electromagnetic pulses from exploding bombs damage my videotapes?"