If you ever listen to choral music from the Republic of Georgia (that's the one in the Caucasus Mountains, not the Southeastern U.S.), and listen in particular to songs from the region of Guria, you'll hear "krimanchuli," which is a controlled yodel supplied by the tenor on top of two other vocal parts. The most easily accessible album is possibly the Rustavi Ensemble's _Georgian Voices_ on Nonesuch, but there are many other recordings on other labels. In particular, listen to a song called "hassanbegura" which is actually a traditional ballad sung in traditional Georgian style--which involves a trio and a chorus, and the top voice of the trio yodels his way above narrative text provided by a middle voice, while a bass voice offers a ground that's a sort of bass yodel.