I will have to agree with Tim. Popping is caused by a faulty seal of the tip to head seat. "pop, pop, pop" it will continue to get worse. Everytime it pops you get a flame kick back to the mixer, eventually it will burn out your mixer.
Make sure your tip nut is snug. Sometimes you can tighten it down a little more and stop the popping. I have had Victor tips straight out of the box, last 2 uses and then be junk.