or if i shut the door hard it may do the same
I assume this is only when the upper unit is on and heating.
I think something is loose and causing a short ,What do you think?
I think you are right but finding it is going to be a pain.
If the above I assume is correct then I would concentrate on the wires that have power only when this unit is on.
You will have to do a slow and complete inspection of each wire's insulation.
Would also check the frame for signs of an arc.
If you hear an arc or smell ozone at the oven when it pops the breaker then you know you have an intermittent dead short somewhere.
Gene may have a much better feel for this than I do.