Diagnosis
Air is getting into the dispensing line. The most likely culprit is a low water level in the reservoir, causing the dispenser to suck air along with water.
How to Fix It
Keep the reservoir more than half full. The gurgling is the dispenser pulling air from the top of the reservoir as the water level gets low. Refill it before it drops below the 10-cup line.
If That Didn't Work
Check that the black dispensing spout is fully snapped into place on the inside of the reservoir lid. If it's loose, it can draw in air there.
Heads Up
This noise is generally harmless but annoying. It's a design quirk of this model. Consistently running it nearly empty won't damage it, but you'll always hear the gurgle.