Help! Poor Runing and Electric Buzzing Sound

Hi people... sorry to start off my first post with a problem.

I have a 1.4 petrol Skoda Fabia which has been running fine, now when i start the car its runing poorly and a bit shakey, almost as if one of the leads arent working or something. The main thing i notice though is that when i turn the ignition to turn the elctrics on and not actually start the car, if i run round to the engine, theres an electronic buzzing noise(the only way i can explain it) which goes on for about 4 or 5 seconds. Its to the right of the casing that covers the engine. Any Ideas?

Thanks