I take it to be Kul-hul-hoo,
with the initial "Kul" sound made in a similar way to the noise that Gollum made in The Hobbit (as described in the books, not as portrayed in the LOTR films, where it was more of a hacking cough).
( monster munch person, man, woman... camera... TV?, Fri 8 Jul 2005, 13:33, archived)