As per the OP it's definitley the screen (does it in the dark too!).
As it happens I did some research which pointed me to a partial fix - the screen on the Aspire is VERY bright so I usually operate it wound down to almost min brightness.
I now know that the screen brightness is set at whatever I had it on last in Windows. In Windows no flicker is visible irrespective of the brightness, but I read that some LED panels modulate the frequency of the backlight to achieve dimming which can lead to flicker.
I turned the brightness up a few notches in Windows and rebooted to TC and the flicker is now almost absent - certainly I can use it without discomfort.
I assume the dimming method is controled by the driver which for the TC instal introduces the flicker at low brightness levels (?)
Now if only I can control the brightness in TC .... and find where my Thunderbird installation has dissapeared to
I'd be sorted.