Nessie and Noise on my XPS 8500

I have been unable to configure the Blue Nessie USB microphone to record in Audacity or Camtasia Studio without an accompanying background buzz. (Windows 7 Sp1 x64 system).

The problem is not the microphone. I can get a clean recording using Windows 7's built-in Sound Recorder, and I have tested the mic on my wife's Inspiron laptop with no problems.

I have updated Windows drivers, changed various settings in the Dell Sound Manger and Hardware Sound settings via Control Panel and tried the unprocessed and processed sound positions on the Nessie.

Nothing works.

Any suggestions?