While inspecting a direct vent HE furnace today, there was a gurgling sound coming from the air gap at the condensate discharge line. I went outside and and checked the vent and intake pipes. It felt like there was way more exhaust being blown out the discharge than air being sucked into the intake. What is happening here? I've never heard the condensate line gurgle like that. I assume that the draft fan is pulling air in through the condensate line. If so, why would this happen and what are the implications of it?