Default screen is trembling (icons and texts) !!

hello everybody

my "Xperia C" after working for few minutes (or after the cpu heats) the screen is trembling and all the icons and texts are trembling


but the confusing thing is when I take screenshot for the screen , everything was good , all of that problem wasn't appear in the screenshot !

the device comes back to normal after I let it without working for some minutes .

I took it to the service center and re-falshed it with the firmware but the problem is still existed !!

please help me
My posts : Sony Walkman Font
- Sony Ericsson Xperia arc S
- - ROM : Xperia Ultimate HD 5.0.1
- - Kernel : LuPuSv16