How do I stop my laptop fan from going on and on and on ?

My problem is quite simple yet it is driving me nuts !! Well, me being a fan of n.c.I.s. I have dvds of the first four seasons and while I’m trying to watch that my laptop fan just starts up for a while then stops then starts and stops and starts and stops and it oes on like that . Since this is happening when I get to a quiet scene in n.c.I.s. Or a very emotional scene it’s ruined because of my stupid fan, then I have to rewind and watch it again which spoils it for me . I went online to another question and answer site and found someone with a similar problem and someone else answered it saying blow into the compartment where the fan is . The person who asked the question voted that the best answer so I decided to try it myself and to make things worse the fan got louder and even more scratchy which in turn makes me a living nightmare to stay in the same room with . I’d really appreciate it if someone could help me to try and stop this . Oh, and one more thing, I don’t need anyone to tell me that I was stupid to blow into the fan compartment .