Noisy kenwood oven?

My built under single kenwood oven is very noisy at front where the air comes out. It sounds like a fan grinding sort of noise, but it happens when using a non fan mode or just the grill. Any ideas? Its heating up perfectly. Do you think replacing the fan at the back of the oven would help? Is there anothe fan in this oven? Sorry no details of oven number and inherited oven with house so don't know when this problem started. Thanks