|Could be your Antivirus, Firewall, or just a bit of handshaking going on to keep the connection alive. The connection is normally maintained even though your browser is closed. It is only an issue if it does it a lot and for a long time.|
If you have a third party Firewall it might show in its records. It would be interesting to know if it continues after you unplug the connection.
One thing you could do is reboot the machine and when all normal activity has ceased type the following from Command Prompt:
Hit Enter key and it will give information on all network activity. Make sure you include the space.
We all live on the same ball.