My mother owns a end of model year 2006 King Ranch Expidition RWD and on cold mornings the power steering pump makes a loud metallic whining noise accompanied by a sound like a mosquito. the resivoir is full and after a few lock to lock turns all noise stops. any ideas on what it could be?

 

As long as the fluid level is correct and no leaks are present....its a normal condition...moving extremely cold fluid through -16*C cold lines requires a lot of pressure...the noise is the pump trying to move the fluid. I have seen pump shafts break due to the stress.

 

No leaks and fluid is full. it scared my mother badly and I thought it was the engine until I turned the stering wheel lock to lock and the noise diminished.

 

The car in question.