Why my CPU makes sound when I open PC?

Hi guys, I have acer PC with windows 7 professional 32 bit version I play games and also use my computer for work and personal use too.But I dont know why my CPU is making sound I mean the sound comes from its fans I think when checked for speed it goes above 50 and then decreases then again its increasing and also the process are running more than 70 is it the cause of sounds CPU making please tell me how to solve this.Thanks in advance
