That’s an estimate. There could be more than two ghosts, says Sandra Nikolajevs, director of Chamber Music Charleston. She’s partly kidding. But partly serious, too. Her ensemble performs regularly at the Old Exchange Building and Provost Dungeon, where they have to schlepp equipment back and forth using an elevator that takes them through the building’s nether regions. If this isn’t the perfect setting for ghostly haunts, nothing is. “I really get a sense that we’re not alone,” Nikolajevs says.