Weird audio problem...stuttering?

[MiG29TangentBoy]

A brief rundown of my stuff:

Asus A8N32-SLI Deluxe motherboard
AMD FX-60 - Socket 939 processor
4x1GB G.Skill HZ PC4000 DDR 500 memory
SilverStone Strider 750 watt Modular PSU
EVGA Nvidia 8800 GTX video card
Seagate 400GB SATA ST3400633AS
Seagate 320GB SATA ST3320620AS
Samsung CD/DVDW SH-S183L SATA DVD drive

I'm using the AC97 onboard audio, as it has always been adequate for my listening habits. But recently, I've noticed a rather odd stuttering during audio and video playback. Windows Media Player and Media Player Classic both skip very briefly every few minutes or so...no matter the source (I've tried mp3, wav, avi, mpeg, flv... heck, even some Flash and Realplayer files).
At first I thought it was the 150G Raptor X drive I was using as my OS disk (it was having freezing and disk errors, thanks WD. That's my second Raptor that has crapped out on me...), but I replaced it with a Seagate and reinstalled Windows XP...same audio skipping problems. Doesn't matter if the file is on a slave drive or the primary drive, same thing.
So...hardware or software? I see nothing in the Event Manager to address this, and the System File Checker comes up clean. Disks are as defragged as possible, and Automatic Defragging is disabled, to rule out interference. I do use K-Lite Codec Pack 3.30 full, as well as Flac Frontend and Ogg Vorbis codecs.
But maybe it's an IRQ issue? I don't want to have to resort to a sound card, as I am hurting for pci slots as it is...I have a Pci-E network card since my onboard lans frizzled a while ago, plus a wireless Pci card and a cooling slot fan to help cool down the 8800GTX. I have an old Soundblaster card from several years ago, but I'm not sure if it would work now. I know heat is not an issue, my case runs cold!

Ok, I'll shut up now. I've blabbed for long enough. Any comments are greatly appreciated.


Edit: No stutter during gaming (Half Life 2, Stalker)...weird.