Whenever I use anything with sound, my mac starts giving strange noises (it doesn't make the noises when I use programmes or apps without sound) - I am thus assuming it is connected with my sound card...

The noise is hard to describe but is kind of squeaky, distorted, high pitched sound coming from the speakers.

Any ideas?... I am thinking of buying a new sound card but I thought it would be worth checking with you guys first...

(It is aMacBook Pro, 17", bought in 2008 - it was brand new back then)