Hi George I just found a similar cause.
.It is being caused by the heated bed electronics (But more complicated than that).
Led was off, just out of trigger range . I am using the CR10S. Turn on the Heated bed, and LED comes on steady until the bed reached temperature and then the random flashing commences. Hmmm OK...so I did another experiment later with a cold bed. I positioned Z height so that LED turned off. The temp in room was 19c. So I set the bed temp to 20C and what do you know.. LED turned on then started flickering and flashing once the bed hits temp and PID kicks in to maintain current temp.
I found a work around. I have the EZConnect plugged into one of those USB adaptors that plugs into mains. That adaptor was plugged into the same power board as the Printer. I moved it to another power board in the room and it is stable and working correctly.
It also seems to work if the EZConnect USB power is plugged into a USB hub instead of a mains charger....however I did have a problem. I plugged the ez connect into the same USB hub that the Cr10 is plugged into to talk to the computer and it Rebooted the CR10 when I plugged the ezconnect USB into the same hub. (after that though it all seems fine and led is stable) . I am wondering if we are getting a ground loop through the EzConnect power?