Q: macbook pro external display flicker issues

I have a macbook pro 13 inch mid 2012 with the Intel HD Graphics 4000 1024 MB graphics card and am running OS X 10.9.5.  A few weeks ago my external display has been flickering severely (horizontal black lines and jumping image) to the point of being unusable.  I have tried different monitors, different cables, different adapters and all the "tricks" on when and how to power up the external monitor. I even tried positioning the cable in different orientations (thinking there may be a loose connection on the macbook side) and I still have the same problem.  The laptop display is fine and stable.  I fear the graphics card is failing or there is a loose connection on the board.  Before I take it in, does anyone have any suggestions?