Understanding how the typical 'frost-free' fridge works sometimes helps coping with different or louder noises.
As you've surmised (at least here in the U.S.) there's a metal plate or two or a similar device behind a back panel on the freezer side that, when in the "Off" cycles 'gathers' frost since the metal plate causes the humidity always present (especially when opening the door) causes it to condense and freeze on the plates. After a period of time, the plates actually heat up and the accumulated frost thaws and drips won the channel behind the covering plate to finally exit though a drain hole in the bottom of the freezer section into a shallow but sizeable 'tray' where it's supposed to evaporate. (The hole sometimes plugs up causing a puddle of water and ice at the bottom and the tray is meant to be cleaned periodically to eliminate mold and smells).
On the other hand, the freezing temperature air that is produced by the fridge comes in only on the fridge side but then is routed through an electrically (usually) controlled smallish door between the freezer and fridge. The opening is modulated by a thermostatically controlled device to attain the "set" temp on the fridge side. There's a blower that moves the air and this can be fairly noisy and is, what I suspect, you're hearing.
If both sides are working properly as to temperatures, you should be Ok once you acclimate to the newer noise...