Hum. You could have bubbles in your power steering line. I don't really know anything about this, but it seems to me the oil and air both expand when they get hot right? Therefore if it was cold, there would be a lack of pressure when you turned the wheel, but when it was warm there would be more pressure within the hose and you might not feel the air as much. However, as I said before, I am only guessing and I know nothing about power steering. I know that power brakes sometimes need to be bled to get the air out of them; could power steering be the same way? Either that, or you might need a new belt, that's the squealing noise, I suspect, that's what it was on my dad's geo. But again, I don't know anything about this... Who knows. Maybe your power steering is actually a squirrel who doesn't work very hard unless the engine is hot to 'encourage' him and when you turn the wheel he is grumpy and squeaks at you in anger. Who knows.