It could be loose chainring bolts...tighten those down.
It could be the eccentricity of your chainring/cog, which causes a variation in chain tension and it'll click. It's a common problem, Sheldon Brown has a method to fix that.
It could be your chain, clean and lube.

FWIW, I have a loose ball bottom bracket and it actually spins smoothly...it is not likely that it is causing the noise.
(Note: I have my own tools to maintain it though. )