Your alternator relay is well worn from play. It is engaged 50% of the time. Mine was buzzing too. I adjusted the coil in the mount, that helped a bit. You can barely hear it when the playfield is down and the door is closed. If it bothers you that much, replace the coil.
It is a must that you replace the fuse holders. I posted some parts I used to replace mine. If you need more detail, PM me.