My name is Daniel, and I will try and help you today. When you say there is an audible sound, do you mean as if it should be heating? have a good look round the door seal for anything that may be stuck to it, and also check the door for any damage. As for the sound coming from the back occasionally, have a look and see if anything has dropped down the back inside.
nothing amiss with the door and nothing dropped down the back.
i would have checked these as a matter of course.
when the until is switched on the light comes on in the oven and the sound i am referring to is the normal sound that microwaves make , like a fan sound.
what is the source of the power ?, is it a bulb or something similar that has blown or something?