Speakers

Hello,
Please help, i bought 2 speakers for my laptop, in the beginning it played fine now when i listen with windows media player after 1-2 min. it starts making a scratching noise when i change the song it plays fine and a gen after +-1 min. it starts again making that interrupted scratching noise, and even if i watch my emails but when i watch a dvd it's fine, what can i check or download to fix this problem,i guy at a computer store told me i must download audio and video codecs but I'm not getting that right, there is so many to choose from and what do i do then pleeaaaasssseeeee help thx.