Can you narrow it down a bit?
Is the traffic just wifi traffic between PC and router / access point (and other PCs), or is it going out to the internet?
It's easy for me to see, because my cable modem is separate from the router. No flashing lights on cable modem = no internet activity, but there may still be traffic on the LAN, between PCs, so flashing lights on the wifi router.
Windows is "chatty", shall we say! Especially with things like UPNP and Bonjour, to mention but a couple.
I rarely see internet traffic that isn't directly associated with an "interactive" internet session.
But then I don't allow anything to auto-update, except Sophos (and that only at startup).
SD