Why is the bottom bracket on my BMX bike popping?
I say this every single time a question pops up like this concerning a new bike. If it's new...IT'S UNDER WARRANTY! If you mess with it yourself, you may just VOID the warranty. Internet sale or did you buy it from an actual bike shop? If bought from a REAL bike shop - take it back & have them look at it. Any work needed will be (or should be) FREE! If an internet sale, contact the seller & ask for a list of authorized repair shops in your area. The seller should cover the cost of any parts needed - if any. You'll most likely have to cover labor cost.
How tight is the chain? A chain that is too tight can cause a popping sound and can damage wheel and bottom bracket bearings
Maybe you have popcorn trapped there??