From Dictionary of American Regional English by Frederic Gomes Cassidy and Joan Houston Hall (Cambridge, Mass: Belknap Press of Harvard University Press, 1985):

Eephing vbl n [Echoic] Cf hoodling, whoop B
Creating wordless vocal music made up of nonsense syllables and percussive sounds; also n eaf such music.
1971 in 1978 I'm on My Journey Home (Phonodisc) wTN, [My maternal uncle] called it hoodlin'; they call it eephin' now. He [=the uncle] got it from somebody at a dance up at Dyersburg, Tennessee. 1978 Wolfe I'm on My Journey Home 2/1, [Liner notes:] Eephing (or hoodling) is one of a number of vocal-percussive effects still found in the mid-South....[It can be]...created by tickling...[the] throat...altering...[the] mouth cavity...tapping the cheeks....It has been reported in Arkansas, Kentucky, and Mississippi....Eephing has also been found among Afro-Americans. It is customarily performed informally in relaxed social situations. 1978 Dance Shuckin' & Jivin' 323 VA [Black], Have you ever heard this thing called "The Eaf"? Ee-poop-se-de-da-pa-de-da....Well, Bill Robinson [1878-1949, also known as "Mr. Bojangles"] and I used to go around and say that thing [=a long rhyme]...And then we start singing, "Ee-doop, se-da-da-pa-de-da-pa-pop!"