micro hums loudly and turns on by its self when door is closed, have replaced transformer. diode, hard board, magnatron

Hi. It sounds like you have a faulty door switch causing it to run when the door is shut. The loud noise could the hood or control fan motors, or possibly the turn table motor. Run the hood fan by itself to confirm or eliminate the noise coming from this part. Also, turn the turntable on and off to verify this part as well. I have attached links to purchase the door switches. There are 3 different door switches to test. If you need any further help please let me know.