1no object To sniff or snort; to make any of various snuffling and slobbering noises like those of an animal eating greedily. Hence: to eat greedily (also figurative).
2with object To consume or use rapidly or in large amounts; to eat greedily; to grab or snatch.
1980s; earliest use found in Playboy. Perhaps imitative, or perhaps a blend of snarf and either snaffle or snuffle.