Your system idle process runs anywhere from 97-99% when Idle. but dont forget when your Idle you are using 0% CPU usage if you have a dedicated video card. That 97-99% reading in the process list is telling you that the system idle process is using 97-99% of the 0-1% of the total cpu usage.
Also if your sound is glitchy, make sure to tweak your buffer time on your sound. You might be having buffer under or over runs