Realtek HD Audio annoying crackling/popping sounds. Nothing's helping!?

I had some old Altec Lansing speakers, some GE speakers, and some generic speakers, now i've got brand in' new Logitech HD speakers, and my computer still has an annoying Popping/crackling sound. It is prominent inside games like Flight Simulator and GTASA, but in GTA SA, the audio is distorted. But in normal computer use where no sound is being transmitted to the speakers, i still hear the crackling/popping. All of these speakers experience this. It's not the speakers' fault, it's something to do with my computer, How do I solve this? I've already got the newest driver for my computer, Realtek HD Audio Driver. This has been going on since I got the computer in 2006, so even with the original driver, this happens. is it my Soundcard? This sometimes will go away for a while and then will come back.