I locate the source of the popping noise to be around the hub. So far I think I lubricated everything I can get my hands on. The noise is constant and it happens at all gears. I know it's not the chain because I fixed it yesterday when it was clicking, now the clicking noise is gone. I know it's not the crank neither because I lubricated the nuts and bolts there too. Also I put my ears next to the crank and the noise doesn't come from there. I want to ask the question here before I bring it to the shop because I run out of things to lubricate or maybe it's something I have no idea about.