I eventually discovered that my problem was a dying hard drive.  The reason the disk was getting tied up was that it was having trouble being written to (or read possibly).  When the disk finally died, and I replaced it, my problems were gone.  I am slowly (or not so slowly) replacing all my seagate drives with either Hitachi or Toshiba drives.  I have two computer, two external drives and an 8 drive NAS.  I have had 4 Seagate drives die on me.  So far, the Toshiba and Hitachi drives haven't failed me. I know that Seagate has bought out the Htachi drive business.  I am just hoping that Seagate doesn't manage to botch the superior Hitachi technology. 
Just fixed this issue with a customers Vostro 3750. The latest Support drivers cause DPC latency of half a second at a time once every 60 seconds and a lot more smaller pauses in between. The problem can be seen as mouse cursor is stuck for a moment and if there's audio, you'll hear a buzzing sound. See more user experiences at: [URL] A correct solution at the moment seems to be disabling the system device Dell Diag Control Device (i.e. DDDriver64Dcsa.sys) until new version is published. Hope this helps someone to avoid all the troubleshooting we had to do... greetings,  THe
A major bug in the latest SupportAssist / Dell Diag Control Device