I have been having this issue with the pmdg 737ngx where it wont fly straight, this happens randomly and is hard to reproduce. So let me explain what exactly happens, ill have autopilot A engaged with LNAV enabled and its flying the flight plan just fine and all the sudden it will start almost weaving in and out of the magneta line, sometimes it will just turn to one direction though. Ill make a hard turn on the yoke to correct it, autopilot disengages but it still wants to turn. I can see in the virtual cockpit the aileron trim is being turned in what seems like random fashion. Unplugging my yoke does nothing to solve this. Then, what seems like randomly, it will just stop turning itself and ill continue on my way. I can see on the fsx calibrate page that my yoke is operating correctly so i am not sure what the issue is here. Weather seems to have no effect on it btw, this can happen with no winds.