Speakers crackling>>??!!?

I have a brand new set of dell surround sound speakers (a525) and the left speaker seems to make a small sort of crackleing sound, i though it was our wireless but it still does it when the wireless is all off and its only the left speaker. Our pc is very old *(dell xps d300) from 1997 but it still runs fine and i have upgrades ram and hard drive., what is this speaker noise?!