loud fan one minute

this never used to happen before, i've had my macbook for about a month now. whenever i am using it in class now and it goes to sleep - - when i wake it up, there is a LOUD fan noise for about a minute before it stops. it never happened before - should i get it chekced out? is it something in my settings i can do to change that?

also, how much in a macbook battery in case i wanted to carry a spare one?

The Fan will get much louder when the CPU Temperature rises, not likely that its getting too hot while sleeping so you may consider having it serviced. If you have a Mac store near by, they would look at it for you.