Dual Monitor flashing when editing
So I've recently set up a second monitor to display picture in full screen...

It was playing back clips perfectly with no issues. The problem however occurs when editing clips.
Whenever I Expand clips or shorten them by simply dragging them out both monitors start freaking out by black screening/flashing on and off until I let go of the clips.
There's no issue when moving clips around but the second I go to shorten a video clip or extend an adjustment layer it goes crazy. I've tried to find a fix but have had no luck and am hoping someone here knows the answer.
Thanks.