Whining

My minivan sometimes makes a whining noise, especially when I turn the steering wheel. The noise is exactly the same as the noise that is made when the wheel is turned all the way (locked). The steering does not seem to be affected in any way.
I also need to replace the oil pressure switch (slow leak).
I seem to be running low on coolant although I cannot find any leaks.
I'm not sure if any of these problems are connected in any way.
The whining noise has me stumped.
Hope you can help.