You know, I would check to see if your chain is stretched. A while back I had an odd "clicking" sound coming from the crank area, and it turned out to be an overstretched chain. The extra slack somehow had caused it.

Of course, make sure that your pedals are on securely, and the same with the crank arms. Bottom bracket could be loose, or may even need replacement. But I doubt that though, since those cartridges are made to last longer than a teenager on viagra.