By all rights this scrappy late-night fusion of hip-hop music and short-form improv should have completed its life cycle a dozen performances ago. But six months into an on-again, off-again run at WNEP, The Beatbox shows no signs of stagnation. As eager to please as ever, DJ Rene Duquesnoy looks expectantly at the audience every time he licks his fingers and flips the records on his turntable, and director Zach Ward's six cast members lose themselves in the music and the moment by riffing imaginatively on a single audience suggestion. Typically the themes explored owe more to the conventions of improv comedy than to B-boy culture: a grade-school teacher edits his own tirades by abbreviating the curse words; an elderly British couple stage elaborate sex games on their front lawn for the neighbors' benefit. But the ensemble also rises to the challenge of the closing freestyle jam with a series of animated raps that tie a neat bow on all the evening's ideas. Though the show suffers from a few technical limitations, the group's enthusiasm for the material is infectious--and true to hip-hop's pure beginnings. Yo, anything that makes you feel this good deserves a big shout-out. WNEP Theater, 3209 N. Halsted, 773-296-1100. Through December 19: Fridays, midnight. $10.