Diagnosis
That's the sound of refrigerant moving through the system, and it's usually normal, especially when the compressor first kicks on or shuts off. On some units, the lines can vibrate against the cabinet.
How to Fix It
1) Make sure the unit is sitting perfectly level on a firm floor. If it's tilted, the internal drain pan might not be level, causing water to slosh. 2) Check that the water bucket is fully and firmly clicked into place. A loose bucket can amplify vibrations.
If That Didn't Work
If the gurgling is constant and very loud, or if it's accompanied by a hissing sound, there could be a refrigerant leak or a restriction in the line. That requires a professional.
Heads Up
These sounds are often more noticeable in a quiet basement at night. It doesn't necessarily mean anything is wrong if the unit is otherwise pulling water and cooling the exhaust air.