I did a lot of searching on here and elsewhere to see if anyone had this problem. Turns out its quite common. But in most cases the fix was adjusting the aircon pipes where they come into the firewall, either by putting a zip tie around them on the outside in the engine bay, or bending them a little so they don't hit the heater box on the inside.
My problem wasn't that. So after months of stuffing around I pretty much gave up until. . . . I discovered it was way simpler than that! The heater vent that goes into the driver side footwell was loose. It vibrated and buzzed against the heater box at low rpms and drove me nuts, making the noise seem to come from somewhere else. One zip tie and its fixed.
Sounded just like it was coming from the upper middle of the dash. Who knew!
Anyway, with all the hunting I did I figured someone else somewhere is probably just as pissed off as I was, so this is now recorded for posterity.
Dashboard buzz - vibration. Fixed!
