How can I cure a noisy fan on my Dimplex BZT20?

I have a wall mounted Dimplex BZT20 electric fire which is 18 months old. It has developed a loud noise when the fan is switched on. It still produces heat but the noise is unacceptable. I have cleaned out the vents as best I can and can see no blockages or signs of damage. I have contacted my supplier who was not interested. What can I do?