barking head
n. A pundit or commentator who speaks in a loud voice and whose comments tend to be abrasive, aggressive, and partisan.
Try finding a discussion of these issues on any news network. The barking heads who usurp the space of public affairs with high-volume jeers are not equal-opportunity offenders.
—Todd Gitlin, “How TV Killed Democracy on Nov. 7,” The Los Angeles Times, February 14, 2001
1988 (earliest)
The sports anchor desk jockeys are still, by and large, a good-looking, well-coiffed bunch of guys. … They're still LOUD, in the age-old tradition of assaulting your eardrums with headline-shrieking staccato sentences. … But, in fact, there is something new going on here. … The barking heads have been nurturing personal styles whose only shared quality is a kind of evangelical furor.
—Rosie DiManno, “The Boys of Yammer,” The Toronto Star, April 16, 1988
This phrase (spied by subscriber Laurie Mullikin) appears to have been coined by several people over the years. For example, it was self-coined (self-coin: "To coin an already existing word that you didn't know about.") by Laurie in 1997 and by Todd Gitlin in 1998. However, the actual first use goes back to 1988.