When the door is closed it makes a buzzing noise, the micro still works and the noise goes away when turned on and used

> the noise goes away when turned on and used
Is it possible that the other noise produced when using the oven are only covering up the buzz?
I think your microwave has two power supplies; one that supplies the low voltages for the display and control, the other for the magnetron. The first supply may be a standard line frequency unit using an iron-core transformer and if these are cheaply made, the laminations can vibrate and cause a 'buzz.' Better transformers are 'potted' so that the laminations are glued together with epoxy and can't vibrate. On later units, the magnetron voltage is produced by a 'switched mode' power supply that uses solid ferrite instead of iron and never vibrate.
If it was my unit, I would take it far enough apart to run a couple of beads of epoxy glue across the laminated transformer to kill the resonance.