I noticed screen flicker couple days ago while texting, at first I thought it wasn't anything serious, then I started noticing few more times, so I started searching online regarding this issue and ended up on this thread. Based on the comments posted here I did following tests:
Note that I had tried changing every setting there was in the phone, I'm pretty sure its not related to auto- brightness, auto-adjust screen tone, nor any other setting in developer settings, etc.
1) Thought it was due to stock messaging app, so I downloaded go sms pro and played around with it, noticed flickering again.
2) Then I thought it might have something to do with the sending of sms altogether? So I tried typing on Gmail app, still same flickering, tried on stock email app, flickering again.
3) I thought it might have something to do with the stock samsung keyboard after all, so I downloaded go keyboard, and tried typing long sentences in stock email app, gmail and stock messaging app, still same flickering.
4) Then I uninstalled everything I had installed and just typed in S Memo using default samsung keyboard, no flickering. I tested for straight 10 minutes, didn't notice any flickering. If I type somewhere else, screen flickers..
So I searched more on the internet and came to know that lot of people with different android phones also have this problem, now I'm guessing that the problem might be due to the sending of key press signals to the OS keyboard event handler, not sure I could be wrong, it can be something else as well. But it still does not explain why it does not flicker while typing in SMemo, or may be I missed screen flicker during that 10 minute test? I tied typing in Smemo many times though, I didnt notice any flicker but it did on any other app.
Sigh, my first smart phone and I get this problem. So try performing above or similar test guys and let us know your results, also try testing in SMemo.
tl;dr :
Smemo = no flickering - tested 5 times.
Gmail = flicker
Messaging = flicker
Email = flicker
Go SMS Pro = flicker
Go Keyboard = flicker
Conclusion : software issue, not hardware(for sure)