Your first command won't affect your bandwidth usage. Can you tell if it's incoming or outgoing bandwidth? Can you tell what port it's happening on?
Try "netstat -ltup" which will give you all your listening tcp and udp sockets and what program is running them. Check those programs log files. Have you checked your webstats? Have you maybe been slashdotted or something similar.
Switch off all the programs you don't need, for those you do need but the world doesn't need to see, protect them with a firewall.