"Sticking" CPU Problem

Hello, everyone. I have a new interesting problem that has me baffled. My sister's Dell Inspiron E1505 laptop has had an issue for a few years that we previously thought was a sound issue. Any music or video stutters every second like clockwork, rendering it useless as a media machine. I finally realized that it's system-wide. For some reason the CPU "spikes" every second. Here are the issues I have noticed:

- Music/Video stutters every second
- Opening Notepad and holding down a key will repeat the key but stick very briefly at the same rate as the music stutter
- Looking at the CPU meter in Task Manager shows constant fluctuation of the CPU between 0-18%

I have tried reformatting XP and installing Windows 7, and the problem persists. Attached is a screenshot of the CPU Utilization meter just after booting. At first the CPU is pretty docile, and then it just starts going up-down-up-down. It never stops after that. Help!

Start with the event viewer. Are there any error messages there?

I browsed the Event Viewer, but didn't get anything definitive. I was trying to find an Error, Warning, or even Event that repeated itself, but I didn't see anything. The only Errors were for minor issues such as Google Update. How can I provide more information for you to diagnose?

Does it do it when booted into SafeMode?

It doesn't appear so, although the audio service is disabled in Safe Mode. I copied a video (and VLC) over to it via a flash drive and ran it, and I didn't notice any spikes. The CPU Utilization Meter in Task Manager looked stable, and holding down a letter key in Notepad looked stable.

Have you tried to disable the audio device to verify that it is the problem?