Check the chain to be sure there isn't a link that's sticking. I had the same/similar clicking noise last year, and finally traced it to a couple of chain links that had become a bit stiff. Going over the cogs in any of the front three gears didn't make any difference. That's how I figured it had to be the chain for that to happen. Sure enough, I found two stiff links that apparently had gotten something lodged internally that was causing it to stiffen up. A good degreasing, cleaning and lubricating, freed the links up and no more clicking noise. Running the chain backwards usually finds any stubborn links in a hurry.