Headphones only pop on my laptop

Hello,
Ok, this is a werid prob an i can't think on how to fix this. I have a dell inspiron 1520 laptop running windows xp home edition, and when i plug my headphones in the jack, they work until the volume gets to about half to full then the headphones start to pop/crackle. I have tried headphones on ipod and a gateway desktop, both times they work on highest volume settings(which were louder than i could get with my laptop). I have tried diff headphones still same problem with them all. The crackle isn't just with music, its everything that comes through. Not sure what the prob could be but i do know that its my PC. Please help if you have had this problem resolved in the past. I have tried to google the problem but nothing came up close to the problem i have. In my sound and audio properties my default device is sigma tel audio.