Good morning, The buzzing you hear is the compressor trying to start. now It may not be a bad compressor but the capacitor that starts the compressor. waht happens in when the compressor trys to start and you hear that buzz the overload on the compressor kicks it off. Its best to have an HVAC tech look at this if you have noexperience with these. Its sounds like that may be the issue but it very well could be the compressor also.