Bent pipes seem to do this worse than straight...
The late auth0r Shelby Foote had this same problem. In an article titled Civil Discourse by Larry O'Connor that appeared in the Fall 1997 issue of Pipes and tobaccos magazine, he states, in part, "...I don't like a curved pipe. For some reason I don't really understand, saliva collects in a curved pipe. For me anyhow. Then it gets to bubbling, like a stew."
Sablebrush52 is absolutely correct regarding drying your tobacco. Moisture is a byproduct of combustion. If your charge is too moist to begin with, then you have a recipe for the gurgles.