OK, you are running with pretty good security so it is unlikely that anybody is connecting to your network and using your bandwidth.
One thing for you to try would be removing AVG completely and then installing Avast Antivirus, and letting it run a boot time scan. You should immediately however run a HouseCall on your system and let us know the results:
Trend Micro HouseCall - Free Online Virus and Spyware Scan - Trend Micro USA