Wow, a lot of P/S problems hey.
Well lets start off with what our first member is saying;
Chances are some Ford guy got lazy putting your new one on and didn't tighten the high pressure line enough, and just that little leak, is putting bubbles into the system and causing a high pitch noise.
I would try to first find the leak, and then figure out what needs to be done to fix it.
I just put a brand new one on my Focus Zetec, and it whined a little while still working the bubbles out, but after about 50 miles the bubbles worked themselves out, and she is now quit, and running good.
max_toney87If you power steering is whining and sometimes completely cutting off, then I would suggest looking around for a line that looks pinched, even check the connection to the actual steering rack, some of the newer focus's have been know to be made with the lines not being totally tightened from factory, But at this point it does seem with it cutting off, and whining, that you will probably want to replace the P/S pump.
You say you are losing fluid? Have you found a leak, or is the P/S pump or rack believed to be eating it?
For anyone who is going to change their P/S pump, here is a How-to from our "How-to directory".