Delonghi ESM465ST Oven Noisy Fan

If it is a fan assisted oven, then you are likely to have 2 fans, an external cooling fan, and a fan inside the oven for ciculating the hot air.
So to answer your query, yes it is a noisy fan you are going to have to establish which fan.
It could be a worn bearing, or the fan blade has come loose.
If it is a worn bearing, thge only cure is a new fan.
Hope this helps with your problem.

I managed to fix it as the horrendous noise like a plane taking off was due to the vibration of the spindle of the "cooling" fan (the long cylinder with blades) rattling in the metal part of the rubber bung in which it sits at the opposite end to the motor end (that spindle is fixed). This is not the fan at the rear of the oven you see when you open oven door which circulates hot air when fan assisted oven is on.
Disconnect from the mains first and then take the top outer casing off my De Longhi ESM 465ST by removing the 6 screws and lift off cover with and the fan was easily accessible. Simply remove the rubber bung at end of spindle and add 1 drop of oil and put it back. It worked a treat and took me all of 15 minutes and saved me buying a new oven.

I had this on my cooker a few months ago. I took the hob off, (quite time consuming, but not difficult) and found the long fan. Atfer needlessly removing the fan, I found one of the spindals/axles had come out and the fan was unsupported. I just puched it back in and it's been fine since.
Hope this helps.