Samsung american style fridge freezer. The fridge started to make a noise like a fan

Question

The fridge  started to make a noise like a fan catching inside the fridge part, on investigation there is a small fan at the bottom section of the fridge where water drains down to what I think would be the  auto defrost, well this was covered in frost and the fan was catching this.I defrosted it then replaced it and it worked fine for about 2 weeks but now it has started again. Any Ideas. Steve.