Kibo informs me that Franklin stated that:

My monitor's display seems to twitch slightly every ten minutes or
thereabouts.

It's just a very small movement but I notice it easily when I am
reading the screen. The movement seems to be mostly in the
horizontal plane. It never used to do this.

As best as one can guess, is this likely to be a fault with the
monitor or with the graphics card?

In order of probability:
(1) Cable isn't 100% seated & screwed in,
(2) Bad cable/connector, at either end.
(3) Bad solder joint in monitor.
Then all the possible electronic faults in the monitor.
Your card is very unlikely to be the cause. If you can, try borrowing
another monitor to rule out the PC/cable.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------