Residents of the nearby neighborhoods hear the unmistakable sound every Thursday night. The vroom, vroom, vroom of motorcycles -- from lightning-fast Japanese models to lumbering Harley-Davidsons -- roaring their way down Bird Road toward, of all places, La Carreta Restaurant. It's there, in the parking lot, that bikers of all ages congregate from 9:00 p.m. until sometimes 3:00 or 4:00 in the morning -- not for drinking or carousing but for socializing. Anybody who rides is welcome. While it's not a club, some members of local motorcycle organizations attend. Begun with two or three enthusiasts around 1996, the group attracts scores of cycling aficionados who talk about everything from parts to politics. Lately the large number of bikes has forced them across the street to an expansive empty parking lot, but if among all the chatting, hunger or thirst happens to strike, satisfaction is just a few steps away.