Once-a-minute lag spikes

I've just finished building a computer.
I installed Windows XP, downloaded my drivers to the factory-new hard drive and put music and games on it.

I was surprised to find out that my games and audio would lag, hiccup and stammer.
I tweaked ram speed, I removed the motherboard sound card drivers, I ran memtest 3.5, I played with everything I knew how to do, which isn't much.

Right now, I'm having the least amount of Hiccups from when I started. However, they occure like CLOCKWORK.

I've done a lot of troubleshooting and note taking. For example, I ran a song with and without the Nvidia spinning logo test (used to check for jagged lines). The audio hiccups coincide with the video hiccups. So, I started doing more tests. I would wave my bluetooth mouse from left to right until the next hiccup happened... it would cause the pointer to float briefly...

It happens during games, during full load and during no load... it doesn't matter. It happens when the only application open is Windows Media Player. It happens when NOTHING is open. I've tracked it on the TASK MANAGER and included two screen shots.

They line up - one with audio and one without audio... as you can see, they line up perfectly and happen exactly 61 seconds apart. (I learned this by watching the time counter on the audio files that played).

On my two core processor, the hiccups only affect the second core by 1%.
On my first core, however, each hiccup causes a 16% spike. While playing music, it causes a 24% spike. While using the Nvidia spinning logo program WITH audio, it causes a 26% spike, but ALWAYS every 61 seconds.

I've tried different audio files at different bit rates. Nothing makes a difference. I've tried changing the timing on my RAM, but the hiccups are still at 61 seconds.

Could it be my power supply? For some reason, I thought that would cause random power fluctuations, not precisely timed ones... I've considered running my system with only ONE stick of ram, then doing it again with ONLY the OTHER stick of ram... But have not yet tried it. Initially, I thought it was the ram, but now I'm starting to think otherwise.

I've watched my process list, but it shows system idle at 99 and, every so often, 'system' will pop up for a second and use '01'. It does NOT show ANYTHING during these lag spikes; I do NOT see any change in processes or their values DURING each spike. I can only monitor said spikes with hardware- IE: by listening to audio, watching video and watching my CPU usage tracking graph.

HOW can I pinpoint this problem? How can I correct it? WHAT cycles every 61 seconds?
Should I be concerned with my processor? I've only JUST done a fresh install - I see no movement in applications or processes, only processor usage and hardware usage.

Thanks in advance...