Creda Cordialle fan oven (48284) noisy operation?

This is an 8-yo cooker which about 2 years ago started developing a noise when in operation both for grill and oven. I thought it was related to the fan until I realised that it occurred when the grill was in use and the fan (at the back) stationary. However, I believe there's another (cooling) fan somewhere perhaps, so wondering if that's maybe the problem. The noise starts variably within 1-5 minutes of switching the oven/grill on, builds in intensity to almost deafening, and stops immediately it's switched off. It certainly sounds like a rattling fan to me. No odd smells or other concerning issues as yet with it. If it is the cooling fan perhaps, anyone any ideas on how big a job that might be to get repaired??