TV Sound turns on randomly

Hello!  We are using a Denon A/V receiver with our Sony TV and Xfinity X1 DVR.  The receiver turns on randomly (usually in the middle of the night, but not always) and starts playing the audio of the tv over our home theater system.  The support team from Denon says there is "something" on the cable box that is causing the receiver to turn on.  Does anyone have any idea what that "something" could be? Both the TV and the receiver are new.  Thank you ... Patti & Craig