stop the hummimg noise in my oven ?

Fan assisted ovens have a fan behind the backplate along with heating elements.These are easy to access and replace.Most problems occur due to build up of grease and grime,The fan motor assembly has brushes these will also wear out.Try giving the housing a tap with something wooden, this usually frees thing up and quietens the motor.However if it becomes impossible to live with, replace the fan assembly.
Belling electric parts are easily available at low cost from partmaster.com or ebay.Just ensure what model you are dealing with before buying.Are you good with a screwdriver?Just make sure the mains is off before poking around with a screwdriver.

John
August 2019