It is normal to hear noises that resemble the sound of running water as your refrigerator is running. These sounds are made when liquid and gas flow inside the refrigerant system. This is not a malfunction.
The sound could also be coming from the water supply if your refrigerator has an ice-maker, or from the automatic defrosting function if your appliance is a no-frost model. Try to determine where the sound is coming from. If it is coming from the freezer area or between the water supply and the ice-maker, the sound is normal and will stop automatically after a while.
If your appliance isn’t operating normally while making this noise, contact an authorised service agent.