What's always helped with our cats and dogs over the years on the 4th, is simply having some "background noises" going within
the house the whole evening, and also, doing our best to shut out the outside world for a few hours.
We have all the doors and windows closed and our air conditioning running (if you don't have AC that might be a problem after an hour or so in this kind of heat, though) which already helps a lot
to dampen outside noises, and then we usually watch movies in the evening (home theater system), so we make sure to crank up the sound just a little bit more on nights like this, and that totally does the trick. Also, in the kitchen, away from the main TV room, we put some music on shuffle in the MP3 player and turn it up decently, and that masks anything out in that side of the house, too.
But yeah, just do all or a combination of these things (it's only for a couple of hours, really), and it will help a LOT. Just shut out the noise of the outside world for a bit! We actually like doing that quite often anyway.