When we run water in bathroom the lines make a popping noise.

Hot, cold or both?

With a single handle faucet you get some hot with cold even in a neutral position. Our guess it's the hot water pipe expanding. Poor clamping is probably the cause.

Tell me more about this popic sound. Is it loud or a soft sound? Is it a popping or a tapping so0und? Does it happen on both hot and cold? Any more details you can give me? Back to you, Tom