|"so i haven't downloaded anything that would cause this"|
If you are connected to a broadband connection you could have gotten something. Run a scan for malware, spyware, trojans, viruses, etc. Also check your system for any recurring scheduled tasks. 20 minutes is not a very long interval but I suppose something could be scheduled that often. Could even be something as simple as a registration.
You can also check the networking tab in task manager to see if there is network activity during those periods. Hit Cntl+Alt+Del to open the task manager.