Based upon the information you've provided I can think of two things that may create the "medium frequency whirring" sound.
1. Low Power Steering Fluid
When your power steering fluid is low the fluid cannot absorb sound and what you hear is the pump possibly going bad as a result. Sometimes, when the fluid is just low there will be audible component ...
Start by getting as much of the oil as you can out of the header tank, then do a thorough flush of the cooling system. If you have a plastic overflow tank you may want to clean it with a bit of detergent if any of the oil got into it.
Dip stick operating range is typically a liter (or quart). I would say this level of oil loss is acceptable. If you can find the source of the leak it would be best to fix it, but it is not going to hurt anything as long as you keep the oil level within the operating range.
There are a few common faults with this vehicle.
The temperature sensor is the most easy and least expensive to change which is on the thermostat housing on the end of the cylinder head above the gearbox.
If fitted with the electrical thermostat this can stick causing the coolant not to reach the radiator but as you said you get the warning as soon as you ...