It might also be a bump on a chainring tooth. I once found a tooth that was damaged at the tip and bent it back with pliers. But it didn't make audible sound.
My chainring is not exactly parallel to the crank so if I'm on the centerline of the chain, it will rock left to right on the chain as I go each full resolution of the crank. It doesn't make a click sound, but more of a swish. When the chain is on an angle the sound goes away since it's rubbing only one side of the chainring.