cnMaestro shows about a gig a day on inactive radios

Is this normal ? I have a couple of radios that the customer has left plugged in (has power, connects to the AP) but there is no Ethernet connection (So there is no customer usage at all). On one radio just to test I put it in bridge mode and disabled the Ethernet port. Yet the radios consistently show about 870MB to 950MB per day or almost 1 Gig per day.