iTunes -- audio is popping, crackling and audio is out of sync with video.

I've had this issue for a year now and its become so annoying that I've stopped using iTunes for my media files but that's not really a solution. Can anyone explain to me what could cause these symptoms?

- audio is popping and crackling
- when playing video, the audio starts crackling and becomes out of sync with the video
- symptoms only happen when iTunes is NOT minimized in the taskbar
- symptoms gets worse when using the mouse to move the iTunes app window
- I've used onboard audio, a soundblaster x-fi gamer, and a HT Omega Striker 7.1 all the same symptoms
- I think this started happening after an iTunes upgrade last year but can't nail it down
- I've swapped out all the sticks of RAM just in case -- same issues
- Audio and video in Windows Media Player, RealPlayer, and VLC work perfectly
- I've tried changing iTunes settings as discussed in other posts but no luck
- Uninstall/Reinstall = nothing

TIA