Generally when using the mouse to dynamically pan (holding down middle button or wheel and move the mouse), there can be flickering as the drawing is being regenerated with each mouse move.
To eliminate that you may either use the arrow keys to pan the design: left, right, top, bottom. Since there is only one command being processed the panning will occur without any flickering (dynamic mouse movements can rapidly send hundreds of commands).
If you wish, you may use the "scroll bar" to move around. Scroll bars are turned off by default, but you can activation them by going to menu: Setup / Options..., and in the view tab check scroll down and check "Display Scroll Bars in Editor". You will need to restart FAB 3000 after modifying this option.