The fan motor in your oven or cooker is almost always mounted at the rear of the oven cavity and blows air forward, over a fan oven element which heats the air, into the oven.
The principal ensures that because of the forced air due to the fan motor, that the oven temperature is more stable and more accurate. In practice with a good fan oven, this is true and the temperature is far more even and stable as well as allowing the cooking of different food at the same time without the transfer of odours or flavours.
The oven fan motor is essentially a coil driving a magnetic stator and usually when an oven fan motor fails it will be open circuit but, it's not quite that simple in some cases.
Normally when you experience noise from the oven it will be due to a fault with your fan or cooling fan motor. It is not uncommon for the cooling fan to be misaligned or damaged on new cookers in transit; this would be identified by a screeching sound as the blades catch the casing. This problem can be addressed by adjusting the motors alignment to stop the noise.
In the case of older appliances the bearings can fail in the motor which will cause a similar issue. You need to correct the problem promptly because the fan element may fail in addition to the motor. This is because the motor turns slower than it should, causing the fan element to overheat. In some cases the fan blades may even "clip" the element, again leading to its premature failure.
Due to the ingress of grease and cooking fat the fan motor can start to run slowly, the friction created by a build-up of detritus materials causing the motor to "drag" can cause hotspots and the premature failure of your fan oven element. It is well worth checking that the fan motor blades turn freely before replacing the oven element.