This fridge freezer (4 years old) is now emitting a loud but constant mechanical noise that sounds like a either a motor with worn bearings / cogs or a fan blade repeatedly striking an object.

Even when set on ECO (-17 and 6) the freezer temperature appears normal but the fridge is over cooling (ice crystals are beginning to form on cooked meat).

If I turn the power off and back on then one of two things happen:

1) The appliance starts as normal and after 15 to 30 minutes the compressor stops and within a short period the noise described above starts and continues ad infinitum until I power off the appliance.

2) The appliance starts but after 30 - 60 seconds everything stops and the control panel shows 'rd', presumably an error code.

With great perseverance i.e. continually restarting the appliance it will eventually stay on but then reverts back to the behaviour described at 1)

The compressor seems to be working OK, though there is a small quantity of water in the reservoir above the compressor.

Before I empty the freezer and gain access to the various components I was hoping another member may be able to shed some light on which component may be at fault.