Comment 28 for bug 24270

for sure it is framebuffer related since I remember that with the
option vga=none (if I'm not wrong) or without any framebuffer module
compiled in the kernel I don't have this problem.

I don't know if I've already told you but there is a fix which is
always the same and is:
go to the console display, go to the X display, go to the console display
at this point the flicker stops, and you can return to the X display.

The flicker happens more when changing among X and the console (for
example if I switch 20 times, there is a good possibility to have the
flicker at one of these tries)