After unplugging unit. Inside fridge back panel will unscrew, all is behind that careful when lifting out, could be some connectors.
The noise will be the fan unit, in that back panel, usual is only one compressor for fridge and freezer, so check your defrost heater is not stuck on, when you take panel off, if the heater element (it will probably be attached to the evaporator coils, the one with a plug on) is hot it is stuck on, and that is your problem, could be thermistor, could be other things. If thermistor fails to fix, temp solution would be to leave the heater unplugged. But it will start to ice up.
SD
February 2012