Hey, so I had this problem for almost 8 months now (my screen started flickering with the lower 75% in September 2017, rendering it hard on the eyes to work on) and tried almost everything available at the time (since my guarantee had been passed already, too).
The problem usually started appearing after running the laptop for a few min after having it shut off for several hours at least, and one can actually hear the screen flicker. So I figured it's a hardware problem.
This solution, at least for now, however, seems to work. There are still some flickers every now and then, but for the first time ever since this problem occurred, the flickering decreased without turning the Surface off for several hours. It is kinda weird tho to have the CPU work so hard at all times. Makes me wonder what other side effects might occur...
I use "Heavy Load", free ware and easy to get. Just started the CPU and GPU stress test. Flickering gone.