OK, K showed me the place where the buzzing things in the attic had tunnelled into the drywall and there was just paint remaining, which could be pressed easily. I got some visqueen, duct tape, wasp killer and a stick. Taped the visqueen to the ceiling, then ripped open the nest with the stick.
Those are NOT carpenter bees, those are wasps. Squirted wasp killer in.
Now it's about 3 hours later. We've sprayed a lot of wasp killer in, and I've used a piece of steel rod to poke through the plastic and rip up their nest. I've pulled out several fist-sized hunks of comb, and there are several hundred dead wasps lying in the pools of insecticide in the bottom of the plastic, besides all the combs and larvae that have fallen out.
I've sprayed a bunch of insecticide up inside the ceiling. There's still a heck of a lot of buzzing, but now it sounds more like a hundred than the entire squadron of bombers that it sounded like before. I'm going to let it sit overnight and see what the fumes do to them.
Eventually I'm going to have to pull down the drywall and insulation, seal up the holes, and rebuild that section. But if I can wait until November or so they'll all be dead anyway except the queen.
K is sleeping downstairs tonight. And probably every night until she goes off to college.