See ya in a couple o' weeks; enjoy the PC-FX game time.
If you want to find the culprit, may I suggest NetHogs? It'll show bandwidth used by each process, though it's for Linux so it may not be useful for you. If you're on Windows, then try CurrPorts. It'll reveal all open ports, which process opened the port, and allow you to close the connection and/or process. Unfortunately it doesn't show which one is being a pig, so you'll have to suss that out for yourself. If all else fails, install a firewall and set it to ask for all outbound connections and don't allow any until you're 100% certain that they're good 'uns. Best of luck.