Its quite normal to see 'letter boxing' when viewing Freeview programmes on a 4:3 TV because the programmes are mostly transmitted in widescreen. To double check, watch the Simpsons on Ch45 because that is transmitted in 4:3 and should fill your screen. To fill the screen (but people will look fat) when receiving a widescreen programme you need to look for a Zoom function.
As to the hum. If the hum goes away when you unplug the Met720 then it is faulty and should be returned. (They are not repairable.)
t
October 2007