Well I have cable net and cable modem with leds for sent and received packets.
Normaly when i don't go to the net and have no internet activity the leds are not shining on the modem (or on the local area conection monitor icon in my sistem tray wich is integrted with modem because the modem is conected to my pc by a network adapter). But they not act in that way, and they are always flickering showing me internet activity.