BleepingComputer.com: Deferred Procedure Latency (DPC) spikes

For whatever reason, whenever I use my keyboard, I will occasionally (every ten seconds to a minute) get unusually high DPC latency spikes in the range of 30k-50k microseconds (about 30-50ms), which causes a noticeable hiccup in sound. It gets extremely frustrating when listening to music or using voice chat. I know for a fact that the spikes do not happen when I don't us my keyboard, I've done rather extensive testing with DPC latency checkers and RATT.

I do have rather high DPC latency when "idle" (wireless disabled, nothing actively running except basic processes) of 300-450 microseconds, but it doesn't have any noticeable effects. My wireless card has some known DPC spiking issues (D-LINK DWA 552), but with the latest drivers it only spikes up to about 5-6k microseconds every minute or so. However, it causes no noticeable issues.

It's an old machine with fairly poor hardware, but I've made it work properly in the past, so it can work. I've tried to do as much research on this as possible but no one seems to have my exact issue. It seems a lot of problems are caused by laptop power saving features or battery managers (it's a desktop), or wireless, but that doesn't seem to be quite the case.

I've tried using a different keyboard (still PS/2 connection) and it had no effect. I think switching to a USB keyboard may resolve the issue, but I'm not confident it will do anything, and don't have access to one right now.

I can operate normally, it's just an odd sound glitch. I can run in a 25 man raid on World of Warcraft with Ventrilo in the background, which can be fairly intensive on every part of the machine including the wireless, and everything will be smooth, except the sound glitches out only when I'm using the keyboard.

Here's a bit of the rundown of the system: http://i44.tinypic.com/vh5760.jpg

I'm 100% sure it has nothing to do with any sort of virus/malware infection.

I have tried tweaking some BIOS options, but they're limited and don't change anything. All drivers are as recent as I can find.

Please throw any advice or troubleshooting you can at me, this is quite frustrating.