2004 chevy impala heater issues

I recently bought this car from a private owner and I did not thoroughly  investigate the heating components because it worked in the setting it was set to. However one day I switched the flow of air from the floor to the defrost setting and it quit working. You can hear a slight buzzing or humming sound start everytime you rotate the dial for the air flow. for example from face to dash or dash to floor. Also they have removed the radio that was in there and just cut the wires Im wondering if maybe they shorted something out or backfed and caused a short..... I have the radio but I could use some diagrams so I can hard wire it back in or open to suggestions and help.