Sound Problem. While listen any music or watching movie, some times the CPU usage goesabove 52%

Question

While listen any music or watching movie, some times the CPU usage goesabove 52% and the sound interputed. Some times its playing mp3 filesfrom HDD too slow while copying some other files in my folder to folder. Whythis happen? I do´nt know whats to do?I have reinstalled my OS. change the hard drive and nothing.I have reinstalled my sound driver from install CD. But still i have the sound problem. I cant get the clear sound, onlyinterputed sound. i dont have any issue with my speaker. please help?