Panhandler, the "duds" are evidently from poor drilling and tenon length, which evidently makes them gurgle. I'm either the luckiest sumbitch or ignorant to the ways of pipe smoking. The only pipe I've ever had gurgle was a, well shit, nothing I can pinpoint. I smoke tobacco dry and I don't freight train. So I don't know. I have empathy, because nobody wants a POS for a pipe.
I can tell you this. I've had pipes that don't fit my smoking style and I've either sold them or gifted them and the recipient has either magically turned the pipe into a champ or they hate me so much they can't speak my name. Either way, I'll never know.