You've probably heard it while driving or watching TV. It's so catchy, chances are you've even sung it in the shower. But we'll bet a silver dollar you didn't know that the country-flavored tag line at the end of Yahoo Inc.'s commercials--an energetically yodeled "ya-hoo-oo-oo!"--is at the center of a thorny legal battle.

Wylie Gustafson, a rancher, roper, and lead singer of a country band called Wylie & the Wild West, says he recorded the yodel for Yahoo's first television commercial, back in 1996, and was paid for that one use. When the cry appeared in thousands of commercials during the next six years, he asked to be paid for its continued use, but was rebuffed.

Now, Gustafson has a copyright on the vocal and has filed a $5 million lawsuit, seeking compensation. He says he tried to resolve the matter informally with Yahoo for three years before filing the suit. Yahoo did not immediately return calls for comment.