Unstable winds aloft

For the past couple of months I have been struggling with irratic winds aloft direction and speed. If I select anything other than Fair WX or Clear Skies from the FSX Wx Options (or any online WX with FS or Active Sky), I have what has become a continuous and constant two degree and two knot irratic fluctuation that causes the airspeed to jump up and down by two knots and the power to respond if the autopilot is engaged. Ultimately the autopilot struggles to hold the altitude. With Fair Wx or Clear Skies selected the direction and speed are steady as are the power settings and the altitude.I am flying the PMDG MD-11 but I find the problem persists with the default aircraft.I have tired first repairing and then uninstalling and reinstalling FSX and the MD-11 all to no avail.My system is Q/Core 2.4 with 8800 GTS. I would really appreciate any help anyone can give me to fix things. Peter.