Hi there - checking back in. Recall that I had tried two different methods of quieting the A-pillars on my March build Impreza (sport ltd). Passenger side I removed the grill (carefully used a flat bladed watch screwdriver and pried up about 1 inch inboard of the sides along the bottom to start the grill, then pried it the rest of the way out (gently!) with my hands). Anyway, for that side I folded felt padding and inserted/jammed it up under the "point" near the clip of the A-pillar cover - which seems to have done the job. The driver's side was more "quick and dirty" to see if this method would also work. There, I just jammed a felt pad between the windscreen and the top of the A-pillar cover. That too seems to have worked. I will probably move to duplicate the passenger side sometime soon since it is less obvious.
Still, good to know we have power over some of the obvious rattles/buzzes.
The link below is an exact copy of the felt pads I am using.
Hope that is helpful.
I think I have heard the deep in the dash rattle but only a few times, so fingers crossed on that one for now.
Over and out.