WIGGLES

This is a problem my IFCS friend has been having. This issue just came up with our aircraft. Whenever the autopilot is engaged, it causes a rudder deflection throughout flight. The movement is slight but noticeable to crew in the back. 3 servo motors have been changed as well as the processor. Cable tension has been adjusted as well. It works for a few flights before returning. All wiring checks good throughout the system. We have a similar problem on a different tail number, but it's on the elevator side. I have a theory that it might be mechanical since the aircraft have been modded for another mission and now have substantial amount of weight added. My idea is that maybe the added weight and/or flight attitude could be affecting the servos or flight surface. We have been dealing with this problem for over a year now and have not heard back from engineering assist requests. Just wondering if anyone else has had a similar problem and what fixed it.