Diagnosing Display Issues - Cables or TV Itself?

TV seems to be having display glitches, both in terms of distortion (horizontal shifts between display lines) or failure (gradient from solid gray to full color vertically, or the bottom half being solid white). Sound is also spotty occasionally. All issues are intermittent and not reliably replicable so troubleshooting is difficult. Seems to happen regardless of connected device. The TV setup is in a difficult to maintain space so I'd like to diagnose if this is a TV issue or an HDMI issue before I buy a new unit or pull the very long cords out.

TL;DR: does this sound like the TV dying or a faulty HDMI cord?