It's the head and how hard you tightened it down. I have found times when my PT2 would simply not have any draw at all, like it was blocked. Other times it was gurgling to no end. I found there's a sweet spot with the head. You have to tighten it down till it cant go any further, and then back it out about 1/8 of a turn, and it's perfect.
Just my two cents.
Just my two cents.