Relevant history: I've previously owned a 2011 15" MacBook Pro which died this year due to faulty graphics card/logic board. After that I purchased a 2016 15" tbMBP which had the serious video glitch issue amongst many other problems. I returned it. Since then I've picked up an apple cert refurb 15" rMBP. It's been working quit well aside from some very minor screen glitches, especially when connecting/disconnecting to my dell 4k monitor. It's not as bad as the 2016 tbMBP glitches. But reminiscent of the minor pixelation and glitches I had with the 2011 throughout its life until it got progressively worse and died a month after the service program was stopped. Is this normal, or should I be concerned?