It will vary depending on the liquid, if it does'nt taste burnt i would'nt worry.
If you have a VV device you can turn the voltage down a touch if the popping noise is annoying you.
Love this topic! Thanks for posting Jefftow. Reminds of my first venture into the vaping world and was the first question that I asked, and my first concern. As those before me have said, popping and fizzing is 'normal'.
It's caused by the e-liquid 'bump boiling' rather than turning to vapour. The popping noise is the bubbles in the liquid popping and the liquid hitting the inside of the coil head.