An alteration of the phrase, "what's happening?"
Its earliest usage dates back to 1992 when Ice Cube (best known for his lead acting role in "Are We Done Yet?") inquired eloquently about the occurrence of a game of craps.
Tre: Whats the haps?
IC: I don't know, but today seems kinda odd
Tre: Do please elaborate while I listen to Footsteps In The Dark by The Isley Brothers