how fix my creda concepplus oven?

when i turn the oven on, after a while say 15 mins ovening the oven makes a noise like Rolf Harriss zing zing metal board twang. them off goes the main circuit braker and all goes out . Leave it then reset it AOK then a few minutes later off again thus the oven takes forever to cook. In fact impossible the res of the cotrols work fine.Is it a fan overload shorting problem, As experts you guys have met this before. I am a DIY man...eg fan knackered, bearing shot , greasy brushes,commutaor wants cleaning etc. All ideas welcomed