"I Don't Want to Know," but believe me, it took me a while to remember the name of the song. Check out all the dirt behind the album on Wikipedia http://en.wikipedia.org/wiki/Rumours:
Every morning — or just about — I wake up with some snatchlet of music in my head. Some days it may take well past lunch for the theme from "What's Happenin'?'" to work its way out and I figure why should I suffer alone?