It's either the rear derailleur or the bottom bracket. It's intermittent and will sometimes make no noise whatsoever then the clicking and clunking noises start. I can feel a vibration in the pedal when the clunk sound takes place so I'm leaning towards the bottom bracket. It can be completely silent then after coasting it will be back. I would hate to think that this is normal as it's very annoying, especially for a bike that was just purchased in September. I've got about 200 miles on it; all of it ridden on pavement.