I've since noticed that I get a momentary spike even when I'm loading a website, especially if it involves Flash.
I'm running Win7, Core2 Duo 2ghz, 4gb RAM, and I've recently been running into a rather odd problem. When I'm either downloading a file or transmitting a large email attachment, my CPU spikes and the computer bogs down considerably. In fact, using The Ultimate Troubleshooter I'm showing that transmitting a file, be it in iTunes, Firefox, or Thunderbird, adds about a 20-40% load on my CPU. With these three programs open my "resting" CPU load is at ~5%. I first noticed it while playing a song in iTunes, and this sort of spike makes the song garbled and causes it to hang repeatedly.
Malwarebytes runs every day, and I've recently used Glary Utilities to clean up the registry, etc. I connect to the internet via the Ethernet jack through a non-wireless router. Any ideas on why this is happening?