It doesn't take the world's most expert ear to hear in the music of Los Pleneros de la 21 something rich and important. Los Pleneros play bomba and plena, the fast, percussive styles of ensemble folk music from the coastal towns of Puerto Rico that exist in interesting opposition to the somewhat more stately and lyrical Spanish-sounding strains that hold sway in the island's interior. The Pleneros sides I've heard showcase a series of terrifically strident and rhythmically subtle solo singers trading short Spanish phrases with a mixed chorus set against some of the hardest-driving two-chord grooves imaginable. The band arrangements, which certainly don't sound written down, give prominent play to three of the world's coolest musical instruments: cuatro (actually a ten-string guitarlike instrument, despite the name), melodica, and of course drums. Plenty of drums. This is Caribbean dance music a good deal faster and less slick than the salsa/mambo stuff it helped spawn, and Los Pleneros play it with a freshness that makes it sound like it just came up out of the ground. Saturday, 8 PM, the Vic, 3145 N. Sheffield; 472-0449 or 525-7793.