What kind of flickering?
If you're seeing it on water or distant objects, get the Develop menu visible (Ctrl-Alt-Q if you don't see it), then use Develop>Rendering>Object-Object Occlusion to turn off that feature (Ctrl-Shift-O as a shortcut).
Occlusion culling is intended as an optimization, but in SL, in practice, you usually won't notice much of a difference.