Yodeling (or yodelling, jodeling) is a form of singing that involves singing an extended note which rapidly and repeatedly changes in pitch from the vocal or chest register (or "chest voice") to the falsetto/head register; making a high-low-high-low sound. http://en.wikipedia.org/wiki/Yodeling
p/s: kat malaysia ni saper jer penyanyi yang boleh buat cam ni?