In alt.home.repair, on Sun, 22 Oct 2017 21:16:45 -0700 (PDT),
wrote:

Do a search for sound absorbing paint. You'll find several.

I hadn't heard of this but for the sake of these two posts, I'll assume
it works:

I'll admit I haven't looked, but unless he's going to paint his windows,
doesn't he have to paint the rooms that face the windows?

I think the sound is coming in through the windows, not the walls, so
even if his house is painted and he paints the house outside, won't that
just change how much is reflected back at the street, not how much comes
into the house?