Diagnosis
Yes, this is normal during the defrost cycle. The unit temporarily reverses to melt ice off the coils, and you're hearing refrigerant moving through the system.
How to Fix It
No fix needed—it's a design feature. The noise typically lasts 5-10 minutes and occurs when the unit has been running in cooler conditions (below 70°F/21°C). It will return to normal fan/compressor noise afterward.
If That Didn't Work
If the gurgling is constant or accompanied by a hiss, you might have a refrigerant leak. This is a sealed system—do not attempt to fix it. Contact Vremi support, as this requires a professional technician.
Heads Up
Distinguish this from a loud rattling or grinding, which points to a loose fan or foreign object in the fan housing. Gurgling/bubbling = normal operation. Grinding = needs inspection.