Replying to this old topic: I think I found the cause of the annoying buzzing sound. This is on an European Mondeo, MY 2015, manufactured in 2016.
Below the glovebox, above the passenger's feet, there's a plastic 'tray' which hides the lower part of the glovebox. This tray is held by two 'fishbone' plastic clips, which are inserted in metallic plates welded to a steel beam. These small metallic plates are probably the issue. I just used a plastic zip tie pulled tight around each of them and the buzz seems to be gone now.
