Whoa! 70 to 3000, that's a big bounce! As 715 said, try to get at least a testing time for your own to see if the other computers are the culprit. To 715 (or rather to his wife) and glzsdq, too, and whomever it concerns, if some netsite is causing a lot of traffic despite it seemingly looking small footprint, try AdBlock in all browsers in the family. I suppose a Facebook gaming page is full of constantly changing ads coming from various servers which of course affects the available bandwidth of every user using the same router.
Other than that, Plotting the Ping may show reasons outside of your house. You never can tell where between your house and the HTC servers there's a major weather related problem in the connections.