Refrigeratures?

I have a Diplomat APM6855 Fridge/Freezer that came with a new Kitchen from Howdons about three years ago. Recently when I open either of the doors a vibration type noise starts which has become louder week by week. Temp settings and usuage is fine but this noise suggests that something is wearing out. It has been suggested to me that it is the fan but can you advise please and how to repair if within the ability of normal DIY skills. Thanks.