It's hard to say without seeing your bike. But it could be your chain is shot and has a kink or a tight spot. Where on your bike is the sound coming from? I've also heard countershaft sprockets come loose which might cause a popping sound. If you can bring it by I can get it diagnosed for you in no time.
Oh, and thanks Cecil.
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Do you really have to start a thread every time you go on a ride and see a guy with no helmet on?
Does it affect you that much that some random guy 1500 miles away went and paid his own money for a 1000?
Do we really have to fight over who uses the back brake or not?
Do you have to argue over stupid pointless shit on the Internet?