Fan making a loud noise in main oven?

We have had a SMEG A2 for 11 years. Although the bulb in the facia above the small oven went a while ago the cooker has been great. Not fab made quality, the gas rings are impossible to get clean they discolour real easy. I wonder if anyone knows what the problem could be with the main oven fan, it has started to make a loud grinding noise, we have looked and nothing is rubbing against it. Thanks for your time, much appreciated.