How can I fix my AEG Competence oven?

Get really loud vibration from oven - especially when it is cooling down following cooking. Can sometimes stop the rattling if I 'hit' front panel with open hand, but problem recurs on next use. Have replaced fan assembly at rear of oven cavity. Is there another fan in the structure that I haven't yet found or is this the result of some resonant vibration in the oven panels? Drives me to distraction! Cannot seem to be able to find a detailed parts diagram to dismantle with confidence.