I admit, when I first heard the "buuuurrrrr" it seemed clear it could be nothing BUT a fart. Tim Russert certainly doesn't look like a man capable of holding in his farts. In fact, I'm willing to wager that he let one right at the moment this book cover photo was taken.
After reading the update and some of the comments, I realized upon a second viewing it very well could be someone agreeing with him. I do not want to live in a world where Tim Russert DOESN'T FART ON AIR, and so, I refuse to yield.