Chunon... I was not being confrontational. I was only offering a proven tool to test your system. You said 'from time to time', does the same source material look different as a function of time? If the answer is yes, then there is a problem with your set. Simple as that! I am sorry to hear that you have these issues, and of course, you are correct to say that whatever is going on with my TV has nothing to do with yours or your settings!
Good luck on getting resolved!