Well, as a last ditch effort, you could "out annoy" them. Get yourself a boom box and turn the volume up high to a heavy metal station when they start getting loud. Maybe they'll get the point.

Or, even more annoying, put on headphones, plug into your boom box and sing along -- loud and out of key. A woman at the next desk used to do that. Drove me bonkers. But she was so into her own little world, and sounded so bizarre, I couldn't decide whether to laugh or cry !