A series of sounds made using vowels, wheezes and oral 'fart' sounds and set to rhythm. First popularized in Appalachian culture in the 1880's, it was an imitation of the sounds made by various farm animals and is considered the earliest predecessor of beat-boxing. Sometimes combined with hamboning.
Also referred to as 'effing' or 'ephing'.
A sample of hoodling that you can try: "Eee-pfft-(inhale), eye-pfft-(inhale), oh-pfft-(inhale), ooh-pfft-(inhale)