Sorry if this isn’t the right forum but my brand of TV isn’t listed on the main page. Anyway we recently bought a new Hitachi 4K smart tv. Every now and then the picture quality is dreadful sometimes we get white lines on the screen, we've got gold 4K HDMI cables that are connected to our virgin media box. I’ve included a link to the place we’ve bought the TV from and a picture to show what I mean about the picture quality.
Buy Hitachi 50 Inch 50HL7000U Smart 4K HDR LED TV at Argos. Thousands of products for same day delivery £3.95, or fast store collection.