I investigated the peaks that appeared in the F2 LVDT. The position of F2 was around 990um in free. There were not any strange peaks in the spectrum in the SAFE mode.  The peaks appeared in the ISOLATED mode. I changed the setpoint for F2 from 1623um to 1423um. The peaks were still there. I offloaded F2 GAS with the FR to around 1600um. Then the peaks disappeared even in the ISOLATED mode.

I checked the resistance and inductance of the LVDT coils at the feedthrough flange. The resistance of the actuator coil (3-8pin) was very large.