Studio 1737 stalling, "sputtering" especially in audio

I reformatted my Studio 1737 and did a clean install of Windows 7 Pro yesterday, but am having a problem with it "stalling".  It didn't do this before reformatting so I'm thinking I installed an incorrect driver?

About every five seconds or so, it's like the hard drive is trying to access something because the system will stall -- if I'm moving the mouse or something, it will hang for about 2 to 5 seconds and then jerk back to working.  

It's especially noticeable when audio is playing back.  Every 2 to 5 seconds, the audio will have almost a static quality and skipping, then resume playing.

I've noticed it happens a lot more when I have, for instance, iTunes open in the background, but running a second audio playback program such as ExpressScribe.  iTunes won't be playing but it will still skip.  Also I've noticed it when just one program is working.

Any ideas on how to correct this, other than reformatting the entire hard drive again?  I installed the drivers from the Dell Support site, especially the RICOH driver and the touchpad driver.