We noticed a lot of bandwidth being used by an Apple TV 2.  Which was odd, because it was just sitting idle.  We never did anything with it, yet it was sucking down 3 Gb of bandwidth daily.

Over a month, the usage followed this wave pattern.

The OS was up to date, there were no web-enabled screensavers, nothing going to this device.  Yet it continued to suck bandwidth.  The solution ended up being performing a full restore to factory defaults and reconfiguring it.  Now the device is happy, using just over 100k in bandwidth daily.