Sound Quality problems with PCI sound card. Only starts 30 seconds after startup

[Pealy]

This is a re-post of "Sound Quality Problems ONLY When No Monitor Plugged In" as the monitor seems to be a red herring.

I am using a VIA EPIA CN10000 with a Laptop HD and a Terratec EWX 24/96 sound card. There's nothing else. I'm using Windows XP Pro SP2. To help test I've a added an MP3 to my windows Startup. When the PC boots up the MP3 starts playing as you'd expect and all sounds fine. After around 30 seconds the quality deteriorates with lots of clicking and popping. This always happens at about 30 seconds after bootup and once it's started it never goes away. I can get it closer to a minute by changing some of the BIOS options to do with IRQ & Plug-and-Play but can't get rid of it. If I enable and use the on-board sound instead of the sound card there's no problem at all. There are no IRQ conflicts but the PCI card is sharing a channel with on-board items like the network card. I've re-installed from a formatted HD about 10 times, tried a bigger power supply, tried plugging the soundcard directly into the board instead of using a riser, I've fiddled with every BIOS setting etc. I know the card works and everything used to be fine with the same setup but an older VIA EPIA board.

Any ideas? The only solution I can think of is buying a USB sound card but I'd much prefer to keep the Terratec if I can.

[Pealy]

Update - Bought a M-Audio Transit USB sound card, it's doing the same thing so it's definitely the motherboard. Looks like it'll have to go back.

[Clunk]

Did you try a pci graphics card?

[Pealy]

Did you try a pci graphics card?

No, I didn't have one lying around and couldn't quite see the point of spending money (even a fiver). The USB card was something I wanted anyway so it was a worth trying.