At long last, the question burning a hole in my brain, keeping me up nights, making it so that I can't eat, can't concentrate on anything else - that question has been answered.
Ages ago, long before the snow fell, I asked in this post (see item IV) what the music was in a certain car commercial. I got no answer. Now I know.
The song is "Krusty" by Papa M. Yes, that Papa M: Dave Pajo, of Slint and Tortoise, etc. Makes perfect sense once you know, doesn't it? From the album Whatever, Mortal released waaaay back in '99 (does anyone even remember 1999?). All info on this website. There's a video, too, in the MEDIA section.
Now I can sleep at night.
[And thanks, CC, for doing the legwork, i.e. 30 seconds of googling.]