But it doesn't happen when you're not browsing.....
I'd say clean up your browser. If it's IE, delete temp files, try limiting the background processes, and get a full spyware cleaning done. That might help too, as lots of that junk can cause little system hickups.
umheint0's phat setup --> <A HREF="http://home.cc.umanitoba.ca/~umheint0/system.html" target="_new">http://home.cc.umanitoba.ca/