Had the same/similar problem with a Dell XPS 15z. Their response was some bs about realtime audio being a Windows 7 problem. It was either the Wired Ethernet or Wifi driver being the main culprit. Disabling it seemed to fix the problem.

Have a skim read of:
http://forum.notebookreview.com/dell-xps...rk-traffic.html
and the first post here where some good info was collected:
http://en.community.dell.com/support-forums/laptop/f/3517/p/19434026/20091957.aspx