Speakers crackling, Is it a soundcard job?

my speakers have started crackling (getting worse all the time) Ive got the right drivers and tried a few other media players rather than windows. could i have blown the soundcard playing the music too loud or is it just worn out? tried new speakers as well to no avail. i have an acer aspire 5720z laptop with sony megab speakers. how much for a new soundcard / repairs. music is my life. HELP PLEASE.