If you are a confident about opening your laptop , not the best of ideas if you don;t know what your doing, then do that and see if any wires/cables or anything else is right near the fan, also check if the fan is wobbling a lot as it might have been knocked off the rotating pivot it is on. If you don't want to open your laptop see how loud it is while it is not doing anything and if it is loud it is best to return it to the shop you bought it from and see if they can repair it.
Go to the service page for your model. Sony has extended the warranty on a number of models for this exact issue, amny had defective CPU cooling fans. They will arrange a free repair for you if your model is one of the ones affected.