My problems with the slotted (or just Boge in general) was finding so many bad cartos. Never noticed the gurgle thing. Does it do it with a full tank or just half tank and below? Reason I ask is some folks find no issue at full tank and just keep filling at the half mark. Even with the Condor RBA, I notice more gurgling at around the 1/3 mark, so I keep it full. If it gurgles at full, don't know what to tell you.
Seems to be worse when the tank is full but pretty much all the time