Running FSX on a windows 7 computer.  On 727 Captain, both 727-100 and 727-200, autopilot is working fine in all modes but when I reach cruise altitude and engage the altitude hold, the airplane continuously makes minor pitch adjustments at a high rate frequency.  The pitch change isn't more than a degree or two, up and down.  Now this what the altitude hold should do in reality, but it's a jittery instantaneous change of pitch, not smooth and unnoticable like it should be.  The rate of climb gague needle can also be observed to respond to these jittry movements.  This goes away when the altitude hold is turned off and the descent is begun. I also have the 707 Captain and its altitude hold works fine.

Has anyone else had this problem? And has anyone found a fix for this?

Thanks.