I have a General Electric GTS18 fridge -- nothing too fancy. Just yesterday, my wife and I noticed a "tuck-a tuck-a tuck-a" kinda sound coming from just inside the temperature adjustment control housing. If I put my hand up against the plastic under the temperature controls, I can slightly feel the rhythmic "clicks". The temperature controls are at the top of the main refrigerator. I can't really hear the sounds from the freezer, or from outside (or behind) the fridge. The fridge seems to cool just fine otherwise... just wondering what this could be!