I had a 2 year old smart TV with the faster chip by Samsung. Same issue. Tried everything including swapping out the cable box, chasing my modem, changing all of the cable connections and it was still there. So, I bought a new 75" for one room, moved the other large screen to our family room and gave the faulty TV to my son who lives in his own apartment. He connected it to his cable box and guess what....no grey line! I don't think the issue is with the receiver. It is most likely the cable feed into the TV or some kind of radio interference. Try changing the HDMI and coax cables first. Power off your modem, TV and cable box. Change the cables and power everything back on. If that doesn't work, give the TV away. Good luck.