Darran,
You have several plugins installed, and you are using external hardware. My suspicion is that one of these is the problem.
The correct way to diagnose this is to unplug ALL your hardware, remove ALL your plugins except Gizmo, PluginAdmin, and any whose name begins with XP. Then launch the sim and test. Another option would be to download the X-Plane demo, install the Saab, and test.
If the problem is gone, you know it was either a plugin or hardware causing the issue. Place your plugins back in one at a time and test each time. If the problem returns you know which plugin is causing issues. Do the same with your hardware, plug each item in one at a time and test.
Report your findings back here so we can determine your next step.