Power Steering Question ?

Ford cars and trucks do this alot. i've been told that theres air in the lines causing it to whine. i think you have to flush the system out and put new fluid in. i'm not sure how to do it....but i know mine does that same.
 
it might sound a little crazy...but
I had a pump off of my 351 car and I knew it had the ford whine (almost all do) After I put it back on I didn't have any power steering fluid left so I filled it up completely up with Mobil 1 synthetic ATF. The whining stopped.