cooling system

Hi, when I start my car, I can hear a very high sound from running water in pipes. Like if you are filling an empty radiator. Can it be due to air in the cooling system or the aircondition system. Do I need to worry, or is it normal?

The other day I was cleaning out my car and it was hot so I turned up the air conditioning and the fan all the way to high and I heard this really high-pitched noise. Sounds like a planes taking off. This will be the first thing wrong with my lovely car. Has anyone else had this experience when...