My macbook is suddently making a lot of noise, what's happening and how can i fix it ?

Suggest you take it in to an Apple store.

Noise can come from the fan or from the hard drive. If the latter, worst case scenario, your data could be in danger.

Always a good idea, but really critical now is to have a complete back up of your data.

Direct you to the proper forum for MacBook :

Mac OS X Help

ExpressLane

https://expresslane.apple.com/

http://www.apple.com/support/macbasics/

Isolating Issues in Mac OS

http://support.apple.com/kb/TS1388

https://www.apple.com/support/osx/

https://www.apple.com/support/quickassist/

http://www.apple.com/support/mac101/help/

http://www.apple.com/support/mac101/tour/

Get Help with your Product

http://docs.info.apple.com/article.html?artnum=304725