CM500 Ethernet LED non-stop flashing

Thanks for the response.

I understand there are "invisible" background activities going on all the time.  However, the blinking continues during rebooting for the only computer (I've tried 2 different ones) connected BEFORE Windows is loaded.  When I connect the modem to my router, it still flashes after I shutdown all my devices linked to the router, wired or wirelessly.  The AT&T modem I had showed no activities during nights.  Maybe the cable modem works differently from the U-Verse modem?  It's almost feels like the CM500 is initiating the activities.  Tried different Ethernet and coax cables too.  For the time being, it's not affecting my daily use of my computers.  But I want to be sure the modem is not defective and I can still change it from the store if that's the case.