Freezer and fridge seem to be working fine. Occasionally the freezer thaws (ice is wet, sweat on the inside of the freezer door, etc.) then the freezer has a buzzing noise centrally located in the rear of the fridge about where the freezer fan is located. It seems to be working to catch up. It then refreezes everything.

Note nothing in the freezer completely thaws.

What's the problem?

Could be a defective thermostat... or the compressor unit may be dying. If the refridgerant system (freon loop) itself fails its rarely worth the cost to repair.

I assume the seals are good on the doors.

The door seals are in very good condition. No breaches. Anyway to test the thermostat or compressor? Interestly the fridge part works fine. It remains cold. It's just the freezer I'm having trouble with.

The door seals are in very good condition. No breaches. Anyway to test the thermostat or compressor? Interestly the fridge part works fine. It remains cold. It's just the freezer I'm having trouble with.

Pick up an electronic thermometer that has a min and max. One that remembers the hottest and coldest points as well as showing the curent tempature to see how much the temprature is really swinging over the day or week. That's a good start (and they are useful to have anyway)... to be honest, some of the testing and stuff is likely to be beyond what Harry Homeowner can do with what he has in the way of tools.